Matrix derivation in intra coding mode

ABSTRACT

Devices, systems and methods for digital video coding, which includes matrix-based intra prediction methods for video coding, are described. In a representative aspect, a method for video processing includes performing a conversion between a current video block of a video and a bitstream representation of the current video block according to a rule, where the rule specifies a relationship between samples of the current video block and matrices or offset values applied in a matrix weighted intra prediction (MIP) mode during the conversion, and where the MIP mode includes determining a prediction block of the current video block by performing, on previously coded samples of the video, a boundary downsampling operation, followed by a matrix vector multiplication operation, and selectively followed by an upsampling operation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent ApplicationNo. PCT/CN2020/085050, filed on Apr. 16, 2020, which claims the priorityto and benefits of International Patent Application No.PCT/CN2019/082813, filed on Apr. 16, 2019. All the aforementioned patentapplications are hereby incorporated by reference in their entireties.

TECHNICAL FIELD

This patent document relates to video coding techniques, devices andsystems.

BACKGROUND

In spite of the advances in video compression, digital video stillaccounts for the largest bandwidth use on the internet and other digitalcommunication networks. As the number of connected user devices capableof receiving and displaying video increases, it is expected that thebandwidth demand for digital video usage will continue to grow.

SUMMARY

Devices, systems and methods related to digital video coding, andspecifically, matrix-based intra prediction methods for video coding aredescribed. The described methods may be applied to both the existingvideo coding standards (e.g., High Efficiency Video Coding (HEVC)) andfuture video coding standards (e.g., Versatile Video Coding (VVC)) orcodecs.

A first example method of video processing includes performing aconversion between a current video block of a video and a bitstreamrepresentation of the current video block according to a rule, where therule specifies a relationship between samples of the current video blockand matrices or offset values applied in a matrix weighted intraprediction (MIP) mode during the conversion, and where the MIP modeincludes determining a prediction block of the current video block byperforming, on previously coded samples of the video, a boundarydownsampling operation, followed by a matrix vector multiplicationoperation, and selectively followed by an upsampling operation.

A second example method of video processing includes generating, for acurrent video block, an intermediate prediction block using a matrixweighted intra prediction (MIP) mode in which the intermediateprediction block of the current video block is determined by performing,on previously coded samples of the video, a boundary downsamplingoperation, followed by a matrix vector multiplication operation, andselectively followed by an upsampling operation; generating, based onthe intermediate prediction block, a final prediction block based on anadditional operation; and performing, based on the final predictionsignal, a conversion between the current video block and a bitstreamrepresentation of the current video block.

A third example method of video processing includes performing aconversion between a current video block of a video and a bitstreamrepresentation of the current video block, where the conversion includespredicting a plurality of samples of at least a portion of the currentvideo block in a matrix weighted intra prediction (MIP) mode in which aprediction block of the portion of current video block is determined byperforming, on previously coded samples of the video, a boundarydownsampling operation, followed by a matrix vector multiplicationoperation, and selectively followed by an upsampling operation.

A fourth example method of video processing includes performing aconversion between a current video block of a video and a bitstreamrepresentation of the current video block, where the conversion is basedon a rule that indicates whether to filter neighboring samples of thecurrent video block prior to applying the matrix weighted intraprediction (MIP) mode during the conversion, and where the MIP modeincludes determining a prediction block of the current video block byperforming, on previously coded samples of the video, a boundarydownsampling operation, followed by a matrix vector multiplicationoperation, and selectively followed by an upsampling operation.

In yet another representative aspect, the disclosed technology may beused to provide a method for video processing. This exemplary methodincludes determining that a current video block is coded using an affinelinear weighted intra prediction (ALWIP) mode, constructing, based onthe determining, at least a portion of a most probable mode (MPM) listfor the ALWIP mode based on an at least a portion of an MPM list for anon-ALWIP intra mode, and performing, based on the MPM list for theALWIP mode, a conversion between the current video block and a bitstreamrepresentation of the current video block.

In yet another representative aspect, the disclosed technology may beused to provide a method for video processing. This exemplary methodincludes determining that a luma component of a current video block iscoded using an affine linear weighted intra prediction (ALWIP) mode,inferring, based on the determining, a chroma intra mode, andperforming, based on the chroma intra mode, a conversion between thecurrent video block and a bitstream representation of the current videoblock.

In yet another representative aspect, the disclosed technology may beused to provide a method for video processing. This exemplary methodincludes determining that a current video block is coded using an affinelinear weighted intra prediction (ALWIP) mode, and performing, based onthe determining, a conversion between the current video block and abitstream representation of the current video block.

In yet another representative aspect, the disclosed technology may beused to provide a method for video processing. This exemplary methodincludes determining that a current video block is coded using a codingmode different from an affine linear weighted intra prediction (ALWIP)mode, and performing, based on the determining, a conversion between thecurrent video block and a bitstream representation of the current videoblock.

In yet another representative aspect, the disclosed technology may beused to provide a method for video processing. This exemplary methodincludes generating, for a current video block, a first prediction usingan affine linear weighted intra prediction (ALWIP) mode, generating,based on the first prediction, a second prediction using positiondependent intra prediction combination (PDPC), and performing, based onthe second prediction, a conversion between the current video block anda bitstream representation of the current video block.

In yet another representative aspect, the disclosed technology may beused to provide a method for video processing. This exemplary methodincludes determining that a current video block is coded using an affinelinear weighted intra prediction (ALWIP) mode, predicting, based on theALWIP mode, a plurality of sub-blocks of the current video block, andperforming, based on the predicting, a conversion between the currentvideo block and a bitstream representation of the current video block.

In yet another representative aspect, the above-described method isembodied in the form of processor-executable code and stored in acomputer-readable program medium.

In yet another representative aspect, a device that is configured oroperable to perform the above-described method is disclosed. The devicemay include a processor that is programmed to implement this method.

In yet another representative aspect, a video decoder apparatus mayimplement a method as described herein.

The above and other aspects and features of the disclosed technology aredescribed in greater detail in the drawings, the description and theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of 33 intra prediction directions.

FIG. 2 shows an example of 67 intra prediction modes.

FIG. 3 shows an example of locations of samples used for the derivationof the weights of the linear model.

FIG. 4 shows an example of four reference lines neighboring a predictionblock.

FIG. 5A and FIG. 5B show examples of sub-partitions depending on blocksize.

FIG. 6 shows an example of ALWIP for 4×4 blocks.

FIG. 7 shows an example of ALWIP for 8×8 blocks.

FIG. 8 shows an example of ALWIP for 8×4 blocks.

FIG. 9 shows an example of ALWIP for 16×16 blocks.

FIG. 10 shows an example of neighboring blocks using in MPM listconstruction.

FIG. 11 shows a flowchart of an example method for matrix-based intraprediction, in accordance with the disclosed technology.

FIG. 12 shows a flowchart of another example method for matrix-basedintra prediction, in accordance with the disclosed technology.

FIG. 13 shows a flowchart of yet another example method for matrix-basedintra prediction, in accordance with the disclosed technology.

FIG. 14 shows a flowchart of yet another example method for matrix-basedintra prediction, in accordance with the disclosed technology.

FIG. 15 is a block diagram of an example of a hardware platform forimplementing a visual media decoding or a visual media encodingtechnique described in the present document.

FIG. 16 is a block diagram showing an example video processing system inwhich various techniques disclosed herein may be implemented.

FIG. 17 is a block diagram that illustrates an example video codingsystem that may utilize the techniques of this disclosure.

FIG. 18 is a block diagram illustrating an example of video encoder.

FIG. 19 is a block diagram illustrating an example of video decoder.

FIGS. 20-23 show example flowcharts of additional example methods formatrix-based intra prediction, in accordance with the disclosedtechnology.

DETAILED DESCRIPTION

Due to the increasing demand of higher resolution video, video codingmethods and techniques are ubiquitous in modem technology. Video codecstypically include an electronic circuit or software that compresses ordecompresses digital video, and are continually being improved toprovide higher coding efficiency. A video codec converts uncompressedvideo to a compressed format or vice versa. There are complexrelationships between the video quality, the amount of data used torepresent the video (determined by the bit rate), the complexity of theencoding and decoding algorithms, sensitivity to data losses and errors,ease of editing, random access, and end-to-end delay (latency). Thecompressed format usually conforms to a standard video compressionspecification, e.g., the High Efficiency Video Coding (HEVC) standard(also known as H.265 or MPEG-H Part 2), the Versatile Video Coding (VVC)standard to be finalized, or other current and/or future video codingstandards.

Embodiments of the disclosed technology may be applied to existing videocoding standards (e.g., HEVC, H.265) and future standards to improveruntime performance. Section headings are used in the present documentto improve readability of the description and do not in any way limitthe discussion or the embodiments (and/or implementations) to therespective sections only.

1 a Brief Review on HEVC 1.1 Intra Prediction in HEVC/H.265

Intra prediction involves producing samples for a given TB (transformblock) using samples previously reconstructed in the considered colorchannel. The intra prediction mode is separately signaled for the lumaand chroma channels, with the chroma channel intra prediction modeoptionally dependent on the luma channel intra prediction mode via the‘DM_CHROMA’ mode. Although the intra prediction mode is signaled at thePB (prediction block) level, the intra prediction process is applied atthe TB level, in accordance with the residual quad-tree hierarchy forthe CU, thereby allowing the coding of one TB to have an effect on thecoding of the next TB within the CU, and therefore reducing the distanceto the samples used as reference values.

HEVC includes 35 intra prediction modes—a DC mode, a planar mode and 33directional, or ‘angular’ intra prediction modes. The 33 angular intraprediction modes are illustrated in FIG. 1.

For PBs associated with chroma color channels, the intra prediction modeis specified as either planar, DC, horizontal, vertical, ‘DM_CHROMA’mode or sometimes diagonal mode ‘34’.

Note for chroma formats 4:2:2 and 4:2:0, the chroma PB may overlap twoor four (respectively) luma PBs; in this case the luma direction forDM_CHROMA is taken from the top left of these luma PBs.

The DM_CHROMA mode indicates that the intra prediction mode of the lumacolor channel PB is applied to the chroma color channel PBs. Since thisis relatively common, the most-probable-mode coding scheme of theintra_chroma_pred_mode is biased in favor of this mode being selected.

2 Examples of Intra Prediction in VVC

2.1 Intra Mode Coding with 67 Intra Prediction Modes

To capture the arbitrary edge directions presented in natural video, thenumber of directional intra modes is extended from 33, as used in HEVC,to 65. The additional directional modes are depicted as red dottedarrows in FIG. 2, and the planar and DC modes remain the same. Thesedenser directional intra prediction modes apply for all block sizes andfor both luma and chroma intra predictions.

2.2 Examples of the Cross-Component Linear Model (CCLM)

In some embodiments, and to reduce the cross-component redundancy, across-component linear model (CCLM) prediction mode (also referred to asLM), is used in the JEM, for which the chroma samples are predictedbased on the reconstructed luma samples of the same CU by using a linearmodel as follows:

pred_(C)(i,j)=α·rec_(L)′(i,j)+β  (1)

Here, pred_(C)(i,j) represents the predicted chroma samples in a CU andrec_(L)′(i,j) represents the downsampled reconstructed luma samples ofthe same CU. Linear model parameter α and β are derived from therelation between luma values and chroma values from two samples, whichare luma sample with minimum sample value and with maximum sample insidethe set of downsampled neighboring luma samples, and their correspondingchroma samples. FIG. 3 shows an example of the location of the left andabove samples and the sample of the current block involved in the CCLMmode.

This parameter computation is performed as part of the decoding process,and is not just as an encoder search operation. As a result, no syntaxis used to convey the a and R values to the decoder.

For chroma intra mode coding, a total of 8 intra modes are allowed forchroma intra mode coding. Those modes include five traditional intramodes and three cross-component linear model modes (CCLM, LM_A, andLM_L). Chroma mode coding directly depends on the intra prediction modeof the corresponding luma block. Since separate block partitioningstructure for luma and chroma components is enabled in I slices, onechroma block may correspond to multiple luma blocks. Therefore, forChroma DM mode, the intra prediction mode of the corresponding lumablock covering the center position of the current chroma block isdirectly inherited.

2.3 Multiple Reference Line (MRL) Intra Prediction

Multiple reference line (MRL) intra prediction uses more reference linesfor intra prediction. In FIG. 4, an example of 4 reference lines isdepicted, where the samples of segments A and F are not fetched fromreconstructed neighboring samples but padded with the closest samplesfrom Segment B and E, respectively. HEVC intra-picture prediction usesthe nearest reference line (i.e., reference line 0). In MRL, 2additional lines (reference line 1 and reference line 3) are used. Theindex of selected reference line (mrl_idx) is signalled and used togenerate intra predictor. For reference line idx, which is greater than0, only include additional reference line modes in MPM list and onlysignal mpm index without remaining mode.

2.4 Intra Sub-Partitions (ISP)

The Intra Sub-Partitions (ISP) tool divides luma intra-predicted blocksvertically or horizontally into 2 or 4 sub-partitions depending on theblock size. For example, minimum block size for ISP is 4×8 (or 8×4). Ifblock size is greater than 4×8 (or 8×4) then the corresponding block isdivided by 4 sub-partitions. FIG. 5 shows examples of the twopossibilities. All sub-partitions fulfill the condition of having atleast 16 samples.

For each sub-partition, reconstructed samples are obtained by adding theresidual signal to the prediction signal. Here, a residual signal isgenerated by the processes such as entropy decoding, inversequantization and inverse transform. Therefore, the reconstructed samplevalues of each sub-partition are available to generate the prediction ofthe next sub-partition, and each sub-partition is processed repeatedly.In addition, the first sub-partition to be processed is the onecontaining the top-left sample of the CU and then continuing downwards(horizontal split) or rightwards (vertical split). As a result,reference samples used to generate the sub-partitions prediction signalsare only located at the left and above sides of the lines. Allsub-partitions share the same intra mode.

2.5 Affine Linear Weighted Intra Prediction (ALWIP or Matrix-Based IntraPrediction)

Affine linear weighted intra prediction (ALWIP, a.k.a. Matrix basedintra prediction (MIP)) is proposed in JVET-N0217.

In JVET-N0217, two tests are conducted. In test 1, ALWIP is designedwith a memory restriction of 8K bytes and at most 4 multiplications persample. Test 2 is similar to test 1, but further simplifies the designin terms of memory requirement and model architecture.

-   -   Single set of matrices and offset vectors for all block shapes.    -   Reduction of number of modes to 19 for all block shapes.    -   Reduction of memory requirement to 576010-bit values, that is        7.20 Kilobyte.    -   Linear interpolation of predicted samples is carried out in a        single step per direction replacing iterative interpolation as        in the first test.

2.5.1 Test 1 of JVET-N0217

For predicting the samples of a rectangular block of width W and heightH, affine linear weighted intra prediction (ALWIP) takes one line of Hreconstructed neighboring boundary samples left of the block and oneline of W reconstructed neighboring boundary samples above the block asinput. If the reconstructed samples are unavailable, they are generatedas it is done in the conventional intra prediction. The generation ofthe prediction signal is based on the following three steps:

Out of the boundary samples, four samples in the case of W=H=4 and eightsamples in all other cases are extracted by averaging.

A matrix vector multiplication, followed by addition of an offset, iscarried out with the averaged samples as an input. The result is areduced prediction signal on a subsampled set of samples in the originalblock.

The prediction signal at the remaining positions is generated from theprediction signal on the subsampled set by linear interpolation which isa single step linear interpolation in each direction.

The matrices and offset vectors needed to generate the prediction signalare taken from three sets S₀, S₁, S₂ of matrices. The set S₀ consists of18 matrices A₀ ^(i), i∈{0, . . . , 17} each of which has 16 rows and 4columns and 18 offset vectors b₀ ^(i), i∈{0, . . . , 17} each of size16. Matrices and offset vectors of that set are used for blocks of size4×4. The set S₁ consists of 10 matrices A₁ ^(i), i∈{0, . . . , 9}, eachof which has 16 rows and 8 columns and 10 offset vectors b₁ ^(i), i∈{0,. . . , 9} each of size 16. Matrices and offset vectors of that set areused for blocks of sizes 4×8, 8×4 and 8×8. Finally, the set S₂ consistsof 6 matrices A₂ ^(i), i∈{0, . . . , 5}, each of which has 64 rows and 8columns and of 6 offset vectors b₂ ^(i), i∈{0, . . . , 5} of size 64.Matrices and offset vectors of that set or parts of these matrices andoffset vectors are used for all other block-shapes.

The total number of multiplications needed in the computation of thematrix vector product is always smaller than or equal to 4×W×H. In otherwords, at most four multiplications per sample are required for theALWIP modes.

2.5.2 Averaging of the Boundary

In a first step, the input boundaries bdry^(top) and bdry^(left) arereduced to smaller boundaries bdry^(red) and bdry_(red) ^(left). Here,bdry_(red) ^(top) and bdry_(red) ^(left) both consists of 2 samples inthe case of a 4×4-block and both consist of 4 samples in all othercases.

In the case of a 4×4-block, for 0≤i<2, one defines

${{bdry}_{red}^{top}\lbrack i\rbrack} = {\left( {\left( {\sum\limits_{j = 0}^{1}\;{{bdry}^{top}\left\lbrack {{i \cdot 2} + j} \right\rbrack}} \right) + 1} \right)\mspace{14mu}\text{>>}\mspace{14mu} 1}$

and defines bdry_(red) ^(left) analogously.

Otherwise, if the block-width W is given as W=4·2^(k), for 0≤i<4, onedefines

${{bdry}_{red}^{top}\lbrack i\rbrack} = {\left( {\left( {\sum\limits_{j = 0}^{2^{k} - 1}\;{{bdry}^{top}\left\lbrack {{i \cdot 2^{k}} + j} \right\rbrack}} \right) + \left( {1\mspace{14mu}\text{<<}\mspace{14mu}\left( {k - 1} \right)} \right)} \right)\mspace{14mu}\text{>>}\mspace{14mu} k}$

and defines bdry_(red) ^(left) analogously.

The two reduced boundaries bdry_(red) ^(top) and bdry_(red) ^(left) areconcatenated to a reduced boundary vector bdry_(red) which is thus ofsize four for blocks of shape 4×4 and of size eight for blocks of allother shapes. If mode refers to the ALWIP-mode, this concatenation isdefined as follows:

${bdry}_{red} = \left\{ \begin{matrix}\left\lbrack {{bdry}_{red}^{top},{bdry}_{red}^{left}} \right\rbrack & {{{{for}\mspace{14mu} W} = {H = {{4\mspace{14mu}{and}\mspace{14mu}{mode}} < 18}}}\mspace{45mu}} \\\left\lbrack {{bdry}_{red}^{left},{bdry}_{red}^{top}} \right\rbrack & {{{{for}\mspace{14mu} W} = {H = {{4\mspace{14mu}{and}\mspace{14mu}{mode}} \geq 18}}}\mspace{45mu}} \\\left\lbrack {{bdry}_{red}^{top},{bdry}_{red}^{left}} \right\rbrack & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} = {{8\mspace{14mu}{and}\mspace{14mu}{mode}} < 10}} \\\left\lbrack {{bdry}_{red}^{left},{bdry}_{red}^{top}} \right\rbrack & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} = {{8\mspace{14mu}{and}\mspace{14mu}{mode}} \geq 10}} \\\left\lbrack {{bdry}_{red}^{top},{bdry}_{red}^{left}} \right\rbrack & {{{{for}\mspace{14mu}{\max\left( {W,H} \right)}} > {8\mspace{14mu}{and}\mspace{14mu}{mode}} < 6}\mspace{11mu}} \\\left\lbrack {{bdry}_{red}^{left},{bdry}_{red}^{top}} \right\rbrack & {{{{for}\mspace{14mu}{\max\left( {W,H} \right)}} > {8\mspace{14mu}{and}\mspace{14mu}{mode}} \geq 6.}\;}\end{matrix} \right.$

Finally, for the interpolation of the subsampled prediction signal, onlarge blocks a second version of the averaged boundary is needed.Namely, if min(W, H)>8 and W≥H, one writes W=8*2^(l), and, for 0≤i<8,defines

${{bdry}_{redII}^{top}\lbrack i\rbrack} = {\left( {\left( {\sum\limits_{j = 0}^{2^{l} - 1}\;{{bdry}^{top}\left\lbrack {{i \cdot 2^{l}} + j} \right\rbrack}} \right) + \left( {1\mspace{14mu}\text{<<}\mspace{14mu}\left( {l - 1} \right)} \right)} \right)\mspace{14mu}\text{>>}\mspace{14mu}{l.}}$

If min(W, H)>8 and H>W, one defines bdry_(redII) ^(left) analogously.

2.5.3 Generation of the Reduced Prediction Signal by Matrix VectorMultiplication

Out of the reduced input vector bdry_(red) one generates a reducedprediction signal pred_(red). The latter signal is a signal on thedownsampled block of width W_(red) and height H_(red). Here, W_(red) andH_(red) are defined as:

$W_{red} = \left\{ {{\begin{matrix}4 & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} \leq 8} \\{\min\left( {W,8} \right)} & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} > 8}\end{matrix}H_{red}} = \left\{ \begin{matrix}4 & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} \leq 8} \\{\min\left( {H,8} \right)} & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} > 8}\end{matrix} \right.} \right.$

The reduced prediction signal pred_(red) is computed by calculating amatrix vector product and adding an offset:

pred_(red) =A·bdry_(red) +b

Here, A is a matrix that has W_(red)·H_(red) rows and 4 columns if W=H=4and 8 columns in all other cases. b is a vector of size W_(red)·H_(red).

The matrix A and the vector b are taken from one of the sets S₀, S₁, S₂as follows. One defines an index idx=idx(W, H) as follows:

${{idx}\left( {W,H} \right)} = \left\{ \begin{matrix}0 & {{{{for}\mspace{14mu} W} = {H = 4}}\mspace{50mu}} \\1 & {{{{for}\mspace{14mu}{\max\left( {W,H} \right)}} = 8}\;} \\2 & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} > 8.}\end{matrix} \right.$

Moreover, one puts m as follows:

$m = \left\{ \begin{matrix}{{mode}\mspace{56mu}} & {{{{for}\mspace{14mu} W} = {H = {{4\mspace{14mu}{and}\mspace{14mu}{mode}} < 18}}}\mspace{45mu}} \\{{mode} - 17} & {{{{for}\mspace{14mu} W} = {H = {{4\mspace{14mu}{and}\mspace{14mu}{mode}} \geq 18}}}\mspace{45mu}} \\{{mode}\mspace{56mu}} & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} = {{8\mspace{14mu}{and}\mspace{14mu}{mode}} < 10}} \\{{{mode} - 9}\mspace{11mu}} & {{{for}\mspace{14mu}{\max\left( {W,H} \right)}} = {{8\mspace{14mu}{and}\mspace{14mu}{mode}} \geq 10}} \\{{mode}\mspace{56mu}} & {{{{for}\mspace{14mu}{\max\left( {W,H} \right)}} = {{8\mspace{14mu}{and}\mspace{14mu}{mode}} < 6}}\mspace{11mu}} \\{{{mode} - 5}\mspace{11mu}} & {{{{for}\mspace{14mu}{\max\left( {W,H} \right)}} = {{8\mspace{14mu}{and}\mspace{14mu}{mode}} \geq 6.}}\;}\end{matrix} \right.$

Then, if idx≤1 or idx=2 and min(W, H)>4, one puts A=A_(idx) ^(m) andb=b_(idx) ^(m). In the case that idx=2 and min(W, H)=4, one lets A bethe matrix that arises by leaving out every row of A d that, in the caseW=4, corresponds to an odd x-coordinate in the downsampled block, or, inthe case H=4, corresponds to an odd y-coordinate in the downsampledblock.

Finally, the reduced prediction signal is replaced by its transpose inthe following cases:

-   -   W=H=4 and mode≥18    -   max(W, H)=8 and mode≥10    -   max(W, H)>8 and mode≥6

The number of multiplications required for calculation of pred_(red) is4 in the case of W=H=4 since in this case A has 4 columns and 16 rows.In all other cases, A has 8 columns and W_(red)·H_(red) rows and oneimmediately verifies that in these cases 8·W_(red)·H_(red)≤4·W·Hmultiplications are required, i.e. also in these cases, at most 4multiplications per sample are needed to compute pred_(red).

2.5.4 Illustration of the Entire ALWIP Process

The entire process of averaging, matrix vector multiplication and linearinterpolation is illustrated for different shapes in FIGS. 6-9. Note,that the remaining shapes are treated as in one of the depicted cases.

1. Given a 4×4 block, ALWIP takes two averages along each axis of theboundary. The resulting four input samples enter the matrix vectormultiplication. The matrices are taken from the set S₀. After adding anoffset, this yields the 16 final prediction samples. Linearinterpolation is not necessary for generating the prediction signal.Thus, a total of (4-16)/(4·4)=4 multiplications per sample areperformed.

2. Given an 8×8 block, ALWIP takes four averages along each axis of theboundary. The resulting eight input samples enter the matrix vectormultiplication. The matrices are taken from the set S₁. This yields 16samples on the odd positions of the prediction block. Thus, a total of(8·16)/(8·8)=2 multiplications per sample are performed. After adding anoffset, these samples are interpolated vertically by using the reducedtop boundary. Horizontal interpolation follows by using the originalleft boundary.

3. Given an 8×4 block, ALWIP takes four averages along the horizontalaxis of the boundary and the four original boundary values on the leftboundary. The resulting eight input samples enter the matrix vectormultiplication. The matrices are taken from the set S₁. This yields 16samples on the odd horizontal and each vertical positions of theprediction block. Thus, a total of (8·16)/(8·4)=4 multiplications persample are performed. After adding an offset, these samples areinterpolated horizontally by using the original left boundary.

4. Given a 16×16 block, ALWIP takes four averages along each axis of theboundary. The resulting eight input samples enter the matrix vectormultiplication. The matrices are taken from the set S₂. This yields 64samples on the odd positions of the prediction block. Thus, a total of(8·64)/(16·16)=2 multiplications per sample are performed. After addingan offset, these samples are interpolated vertically by using eightaverages of the top boundary. Horizontal interpolation follows by usingthe original left boundary. The interpolation process, in this case,does not add any multiplications. Therefore, totally, twomultiplications per sample are required to calculate ALWIP prediction.

For larger shapes, the procedure is essentially the same and it is easyto check that the number of multiplications per sample is less thanfour.

For W×8 blocks with W>8, only horizontal interpolation is necessary asthe samples are given at the odd horizontal and each vertical positions.

Finally for W×4 blocks with W>8, let A_kbe the matrix that arises byleaving out every row that corresponds to an odd entry along thehorizontal axis of the downsampled block. Thus, the output size is 32and again, only horizontal interpolation remains to be performed.

The transposed cases are treated accordingly.

2.5.5 Single Step Linear Interpolation

For a W×H block with max(W, H)≥8, the prediction signal arises from thereduced prediction signal pred_(red) on W_(red)×H_(red) by linearinterpolation. Depending on the block shape, linear interpolation isdone in vertical, horizontal or both directions. If linear interpolationis to be applied in both directions, it is first applied in horizontaldirection if W<H and it is first applied in vertical direction, else.

Consider without loss of generality a W×H block with max(W, H)≥8 andW≥H. Then, the one-dimensional linear interpolation is performed asfollows. Without loss of generality, it suffices to describe linearinterpolation in vertical direction. First, the reduced predictionsignal is extended to the top by the boundary signal. Define thevertical upsampling factor U_(ver)=H/H_(red) and write U_(ver)=2^(u)^(ver) >1. Then, define the extended reduced prediction signal by

${{{pred}_{red}\lbrack x\rbrack}\left\lbrack {- 1} \right\rbrack} = \left\{ \begin{matrix}{{{bdry}_{red}^{top}\lbrack x\rbrack}\mspace{11mu}} & {{{{for}\mspace{14mu} W} = 8}\;} \\{{bdry}_{redII}^{top}\lbrack x\rbrack} & {{{for}\mspace{14mu} W} > 8.}\end{matrix} \right.$

Then, from this extended reduced prediction signal, the verticallylinear interpolated prediction signal is generated by

${{{pred}_{red}^{{ups},{ver}}\lbrack x\rbrack}\left\lbrack {{U_{ver} \cdot y} + k} \right\rbrack} = {\left( {{\left( {U_{ver} - k - 1} \right) \cdot {{{pred}_{red}\lbrack x\rbrack}\left\lbrack {y - 1} \right\rbrack}} + {\left( {k + 1} \right) \cdot {{{pred}_{red}\lbrack x\rbrack}\lbrack y\rbrack}} + \frac{U_{ver}}{2}} \right)\mspace{14mu}\text{>>}\mspace{14mu} u_{ver}}$

for 0≤x<W_(red), 0≤y<H_(red) and 0≤k<U_(ver).

2.5.6 Signalization of the Proposed Intra Prediction Modes

For each Coding Unit (CU) in intra mode, a flag indicating if an ALWIPmode is to be applied on the corresponding Prediction Unit (PU) or notis sent in the bitstream. The signalization of the latter index isharmonized with MRL in the same way as in JVET-M0043. If an ALWIP modeis to be applied, the index predmode of the ALWIP mode is signaled usinga MPM-list with 3 MPMS.

Here, the derivation of the MPMs is performed using the intra-modes ofthe above and the left PU as follows. There are three fixed tablesmap_angular_to_alwip_(idx), idx ∈{0,1,2} that assign to eachconventional intra prediction mode predmode_(Angular) an ALWIP mode

predmode_(ALWIP)=map_angular_to_alwip_(idx)[predmode_(Angular)].

For each PU of width W and height H one defines an index

idx(PU)=idx(W,H)∈{0,1,2}

that indicates from which of the three sets the ALWIP-parameters are tobe taken as in Section 2.5.3.

If the above Prediction Unit PU_(above) is available, belongs to thesame CTU as the current PU and is in intra mode, ifidx(PU)=idx(PU_(above)) and if ALWIP is applied on PU_(above) withALWIP-mode predmode_(ALWIP) ^(above), one puts

mode_(ALWIP) ^(above)=predmode_(ALWIP) ^(above).

If the above PU is available, belongs to the same CTU as the current PUand is in intra mode and if a conventional intra prediction modepredmode_(Angular) ^(above) is applied on the above PU, one puts

mode_(ALWIP) ^(above)=map_angular_to_alwip_(idx(PU) _(above)₎[predmode_(Angular) ^(above)].

In all other cases, one puts

mode_(ALWIP) ^(above)=−1,

which means that this mode is unavailable. In the same way but withoutthe restriction that the left PU needs to belong to the same CTU as thecurrent PU, one derives a mode mode_(ALWIP) ^(left).

Finally, three fixed default lists list_(idx), idx∈{0,1,2} are provided,each of which contains three distinct ALWIP modes. Out of the defaultlist list_(idx(PU)) and the modes mode_(ALWIP) ^(above) and mode_(ALWIP)^(left) one constructs three distinct MPMs by substituting −1 by defaultvalues as well as eliminating repetitions.

The left neighboring block and above neighboring block used in the ALWIPMPM list construction is A1 and B1 as shown in FIG. 10.

2.5.7 Adapted MPM-List Derivation for Conventional Luma and ChromaIntra-Prediction Modes

The proposed ALWIP-modes are harmonized with the MPM-based coding of theconventional intra-prediction modes as follows. The luma and chromaMPM-list derivation processes for the conventional intra-predictionmodes uses fixed tables map_alwip_to_angular_(idx), idx∈{0,1,2}, mappingan ALWIP-mode predmode_(ALWIP) on a given PU to one of the conventionalintra-prediction modes

predmode_(Angular)=map_alwip_to_angular_(idx(PU))[predmode_(ALWIP)]

For the luma MPM-list derivation, whenever a neighboring luma block isencountered which uses an ALWIP-mode predmode_(ALWIP), this block istreated as if it was using the conventional intra-prediction modepredmode_(Angular). For the chroma MPM-list derivation, whenever thecurrent luma block uses an LWIP-mode, the same mapping is used totranslate the ALWJP-mode to a conventional intra prediction mode.

2.5.8 Corresponding Modified Working Draft

In some embodiments, as described in this section, portions related tointra_lwip_flag, intra_lwip_mpm_flag, intra_lwip_mpm_idx andintra_lwip_mpm_remainder have been added to the working draft based onembodiments of the disclosed technology.

In some embodiments, as described in this section, the <begin> and <end>tags are used to denote additions and modifications to the working draftbased on embodiments of the disclosed technology.

Syntax Tables Coding Unit Syntax

coding_unit( x0, y0, cbWidth, cbHeight, treeType ) { Descriptor  if(tile_group_type != I | | sps_ibc_enabled flag ) {   if( treeType !=DUAL_TREE_CHROMA )    cu_skip_flag[ x0 ][ y0 ] ae(v)   if( cu_skip_flag[ x0 ][ y0 ] = = 0 && tile_group_type != I )    pred_mode_flag ae(v)  if( ( ( tile_group_type = = I && cu_skip_flag[ x0 ][ y0 ] = =0 ) | |   ( tile_group_type != I && CuPredMode [ x0 ][ y0 ] != MODE_INTRA ) )&&    sps_ibc_enabled_flag )    pred_mode_ibc_flag ae(v)  }  if(CuPredMode[ x0 ][ y0 ] = = MODE_INTRA ) {   if( sps_pcm_enabled_flag &&   cbWidth >= MinIpcmCbSizeY && cbWidth <= MaxIpcmCbSizeY &&   cbHeight >= MinIpcmCbSizeY && cbHeight <= MaxIpcmCbSizeY )   pcm_flag[ x0 ][ y0 ] ae(v)   if( pcm_flag[ x0 ][ y0 ] ) {    while(!byte_aligned( ) )     pcm_alignment_zero_bit f(1)    pcm_sample(cbWidth, cbHeight, treeType)   } else {    if( treeType = = SINGLE_TREE| | treeType = = DUAL_TREE_LUMA ) {     if( Abs( Log2( cbWidth ) - Log2(cbHeight ) ) <= 2 )      intra_lwip_flag[ x0 ][ y0 ] ae(v)     if(intra_lwip_flag[ x0 ][ y0 ] ) {       intra_lwip_mpm_flag[ x0 ][ y0 ]ae(v)      if( intra_lwip_mpm_flag[ x0 ][ y0 ] )      intra_lwip_mpm_idx[ x0 ][ y0 ] ae(v)      else      intra_lwip_mpm_remainder[ x0 ][ y0 ] ae(v)      } else {       if(( y0 % CtbSizeY ) > 0 )        intra_luma_ref_idx[ x0 ][ y0 ] ae(v)      if (intra_luma_ref_idx[ x0 ][ y0 ] = = 0 &&        ( cbWidth <=MaxTbSizeY | | cbHeight <= MaxTbSizeY ) &&        ( cbWidth * cbHeight >MinTbSizeY * MinTbSizeY ))        intra_subpartitions_mode_flag[ x0 ][y0 ] ae(v)       if( intra_subpartitions_mode_flag[ x0 ][ y0 ] = = 1 &&       cbWidth <= MaxTbSizeY && cbHeight <= MaxTbSizeY)       intra_subpartitions_split_flag[ x0 ][ y0 ] ae(v)       if(intra_luma_ref_idx[ x0 ][ y0 ] = = 0 &&       intra_subpartitions_mode_flag[ x0 ][ y0 ] = = 0 )       intra_luma_mpm_flag[ x0 ][ y0 ] ae(v)       if(intra_luma_mpm_flag[ x0 ][ y0 ] )        intra_luma_mpm_idx[ x0 ][ y0 ]ae(v)       else        intra_luma_mpm_remainder[ x0 ][ y0 ] ae(v)     }     }     if( treeType = = SINGLE_TREE | | treeType = =DUAL_TREE_CHROMA )      intra_chroma_pred_mode[ x0 ][ y0 ] ae(v)    }  } else if( treeType != DUAL_TREE_CHROMA ) { /* MODE_INTER or MODE_IBC*/    ...

Semantics

<begin>intra_lwip_flag[x0][y0] equal to 1 specifies that the intraprediction type for luma samples is affine linear weighted intraprediction. intra_lwip_flag[x0][y0] equal to 0 specifies that the intraprediction type for luma samples is not affine linear weighted intraprediction.When intra_lwip_flag[x0][y0] is not present, it is inferred to be equalto 0.The syntax elements intra_lwip_mpm_flag[x0][y0],intra_lwip_mpm_idx[x0][y0] and intra_lwip_mpm_remainder [x0][y0] specifythe affine linear weighted intra prediction mode for luma samples. Thearray indices x0, y0 specify the location (x0, y0) of the top-left lumasample of the considered coding block relative to the top-left lumasample of the picture. When intra_lwip_mpm_flag[x0][y0] is equal to 1,the affine linear weighted intra prediction mode is inferred from aneighboring intra-predicted coding unit according to clause 8.4.X.When intra_lwip_mpm_flag[x0][y0] is not present, it is inferred to beequal to 1.<end>intra_subpartitions_split_flag[x0][y0] specifies whetherthe intra subpartitions split type is horizontal or vertical. Whenintra_subpartitions_split_flag[x0][y0] is not present, it is inferred asfollows:

-   -   If intra_lwip_flag[x0][y0] is equal to 1,        intra_subpartitions_split_flag[x0][y0] is inferred to be equal        to 0.    -   Otherwise, the following applies:        -   If cbHeight is greater than MaxTbSizeY,            intra_subpartitions_split_flag[x0][y0] is inferred to be            equal to 0.        -   Otherwise (cbWidth is greater than MaxTbSizeY),            intra_subpartitions_split_flag[x0][y0] is inferred to be            equal to 1.

Decoding Process 8.4.1 General Decoding Process for Coding Units Codedin Intra Prediction Mode

Inputs to this process are:

-   -   a luma location (xCb, yCb) specifying the top-left sample of the        current coding block relative to the top-left luma sample of the        current picture,    -   a variable cbWidth specifying the width of the current coding        block in luma samples,    -   a variable cbHeight specifying the height of the current coding        block in luma samples,    -   a variable treeType specifying whether a single or a dual tree        is used and if a dual tree is used, it specifies whether the        current tree corresponds to the luma or chroma components.        Output of this process is a modified reconstructed picture        before in-loop filtering.        The derivation process for quantization parameters as specified        in clause 8.7.1 is invoked with the luma location (xCb, yCb),        the width of the current coding block in luma samples cbWidth        and the height of the current coding block in luma samples        cbHeight, and the variable treeType as inputs.        When treeType is equal to SINGLE_TREE or treeType is equal to        DUAL_TREE_LUMA, the decoding process for luma samples is        specified as follows:    -   If pcm_flag[xCb][yCb] is equal to 1, the reconstructed picture        is modified as follows:

S _(L)[xCb+i][yCb++j]=pcm_sample_luma[(cbHeight*j)+i]<<(BitDepth_(Y)−PcmBitDepth_(Y)),  (8-6)

-   -   with i=0 . . . cbWidth−1, j=0 . . . cbHeight−1    -   Otherwise, the following applies:    -   1. The luma intra prediction mode is derived as follows:        -   If intra_lwip_flag[xCb][yCb] is equal to 1, the derivation            process for the affine linear weighted intra prediction mode            as specified in clause 8.4.X is invoked with the luma            location (xCb, yCb), the width of the current coding block            in luma samples cbWidth and the height of the current coding            block in luma samples cbHeight as input.        -   Otherwise, the derivation process for the luma intra            prediction mode as specified in clause 8.4.2 is invoked with            the luma location (xCb, yCb), the width of the current            coding block in luma samples cbWidth and the height of the            current coding block in luma samples cbHeight as input.    -   2. The general decoding process for intra blocks as specified in        clause 8.4.4.1 is invoked with the luma location (xCb, yCb), the        tree type treeType, the variable nTbW set equal to cbWidth, the        variable nTbH set equal to cbHeight, the variable predModeIntra        set equal to IntraPredModeY[xCb][yCb], and the variable cldx set        equal to 0 as inputs, and the output is a modified reconstructed        picture before in-loop filtering.    -   . . .        <begin>

8.4.X Derivation Process for Affine Linear Weighted Intra PredictionMode

Input to this process are:

-   -   a luma location (xCb, yCb) specifying the top-left sample of the        current luma coding block relative to the top-left luma sample        of the current picture,    -   a variable cbWidth specifying the width of the current coding        block in luma samples,    -   a variable cbHeight specifying the height of the current coding        block in luma samples.        In this process, the affine linear weighted intra prediction        mode IntraPredModeY[xCb][yCb] is derived.        IntraPredModeY[xCb][yCb] is derived by the following ordered        steps:    -   1. The neighboring locations (xNbA, yNbA) and (xNbB, yNbB) are        set equal to (xCb−1, yCb) and (xCb, yCb−1), respectively.    -   2. For X being replaced by either A or B, the variables        candLwipModeX are derived as follows:        -   The availability derivation process for a block as specified            in clause 6.4.X [Ed. (BB): Neighboring blocks availability            checking process tbd] is invoked with the location (xCurr,            yCurr) set equal to (xCb, yCb) and the neighboring location            (xNbY, yNbY) set equal to (xNbX, yNbX) as inputs, and the            output is assigned to availableX.        -   The candidate affine linear weighted intra prediction mode            candLwipModeX is derived as follows:            -   If one or more of the following conditions are true,                candLwipModeX is set equal to −1.                -   The variable availableX is equal to FALSE.                -   CuPredMode[xNbX][yNbX] is not equal to MODE_INTRA                    and mh_intra_flag[xNbX][yNbX] is not equal to 1.                -   pcm_flag[xNbX][yNbX] is equal to 1.                -   X is equal to B and yCb−1 is less than ((yCb>>CtbLog                    2SizeY)<<CtbLog 2SizeY).            -   Otherwise, the following applies:            -   The size type derivation process for a block as                specified in clause 8.4.X.1 is invoked with the width of                the current coding block in luma samples cbWidth and the                height of the current coding block in luma samples                cbHeight as input, and the output is assigned to                variable sizeId.            -   If intra_lwip_flag[xNbX][yNbX] is equal to 1, the size                type derivation process for a block as specified in                clause 8.4.X.1 is invoked with the width of the                neighboring coding block in luma samples nbWidthX and                the height of the neighboring coding block in luma                samples nbHeightX as input, and the output is assigned                to variable sizeIdX.                -   If sizeId is equal to sizeIdX, candLwipModeX is set                    equal to IntraPredModeY[xNbX][yNbX].                -   Otherwise, candLwipModeX is set equal to −1.            -   Otherwise, candLwipModeX is derived using                IntraPredModeY[xNbX][yNbX] and sizeId as specified in                Table 8-X1.    -   3. The candLwipModeList[x] with x=0..2 is derived as follows,        using lwipMpmCand[sizeId] as specified in Table 8-X2:        -   If candLwipModeA and candLwipModeB are both equal to −1, the            following applies:

candLwipModeList[0]=lwipMpmCand[sizeId][0]  (8-X1)

candLwipModeList[1]=lwipMpmCand[sizeId][1]  (8-X2)

candLwipModeList[2]=lwipMpmCand[sizeId][2]  (8-X3)

-   -   -   Otherwise, the following apllies:            -   If candLwipModeA is equal to candLwipModeB or if either                candLwipModeA or candLwipModeB is equal to −1, the                following applies:

candLwipModeList[0]=(candLwipModeA!=−1)?candLwipModeA:candLwipModeB  (8-X4)

-   -   -   -   If candLwipModeList[0] is equal to                lwipMpmCand[sizeId][0], the following applies:

candLwipModeList[1]=lwipMpmCand[sizeId][1]  (8-X5)

candLwipModeList[2]=lwipMpmCand[sizeId][2]  (8-X6)

-   -   -   -   Otherwise, the following applies:

candLwipModeList[1]=lwipMpmCand[sizeId][0]  (8-X7)

candLwipModeList[2]=(candLwipModeList[0]!=lwipMpmCand[sizeId][1])?lwipMpmCand[sizeId][1]:lwipMpmCand[sizeId][2]  (8-X8)

-   -   -   -   Otherwise, the following applies:

candLwipModeList[0]=candLwipModeA  (8-X9)

candLwipModeList[1]=candLwipModeB  (8-X10)

-   -   -   -   -   If candLwipModeA and candLwipModeB are both not                    equal to lwipMpmCand[sizeId][0], the following                    applies:

candLwipModeList[2]=lwipMpmCand[sizeId][0]  (8-X11)

-   -   Otherwise, the following applies:    -   If candLwipModeA and candLwipModeB are both not equal to        lwipMpmCand[sizeId][1], the following applies:

candLwipModeList[2]=lwipMpmCand[sizeId][1]  (8-X12)

-   -   Otherwise, the following applies:

candLwipModeList[2]=lwipMpmCand[sizeId][2]  (8-X13)

-   -   4. IntraPredModeY[xCb][yCb] is derived by applying the following        procedure:        -   If intra_lwip_mpmflag[xCb][yCb] is equal to 1, the            IntraPredModeY[xCb][yCb] is set equal to            candLwipModeList[intra_lwip_mpm_idx[xCb][yCb]].        -   Otherwise, IntraPredModeY[xCb][yCb] is derived by applying            the following ordered steps:        -   1. When candLwipModeList[i] is greater than            candLwipModeList[j] for i=0..1 and for each i, j=(i+1) . . .            2, both values are swapped as follows:

(candLwipModeList[i],candLwipModeList[j])=Swap(candLwipModeList[i],candLwipModeList[j])  (8-X14)

-   -   -   2. IntraPredModeY[xCb][yCb] is derived by the following            ordered steps:            -   i. IntraPredModeY[xCb][yCb] is set equal to                intra_lwip_mpm_remainder[xCb][yCb].            -   ii. For i equal to 0 to 2, inclusive, when                IntraPredModeY[xCb][yCb] is greater than or equal to                candLwipModeList[i], the value of                IntraPredModeY[xCb][yCb] is incremented by one.

The variable IntraPredModeY[x][y] with x=xCb . . . xCb+cbWidth−1 andy=yCb . . . yCb+cbHeight−1 is set to be equal toIntraPredModeY[xCb][yCb].

8.4.X.1 Derivation Process for Prediction Block Size Type

Input to this process are:

-   -   a variable cbWidth specifying the width of the current coding        block in luma samples,    -   a variable cbHeight specifying the height of the current coding        block in luma samples.

Output of this process is a variable sizeId.

The variable sizeId is derived as follows:

-   -   If both cbWidth and cbHeight are equal to 4, sizeId is set equal        to 0.    -   Otherwise, if both cbWidth and cbHeight are less than or equal        to 8, sizeId is set equal to 1.    -   Otherwise, sizeId is set equal to 2.

TABLE 8-X1 Specification of mapping between intra prediction and affinelinear weighted intra prediction modes block size type sizeIdIntraPredModeY[ xNbX ] [ yNbX ] 0 1 2 0 17 0 5 1 17 0 1 2, 3 17 10 3 4,5 9 10 3 6, 7 9 10 3 8, 9 9 10 3 10, 11 9 10 0 12, 13 17 4 0 14, 15 17 60 16, 17 17 7 4 18, 19 17 7 4 20, 21 17 7 4 22, 23 17 5 5 24, 25 17 5 126, 27 5 0 1 28, 29 5 0 1 30, 31 5 3 1 32, 33 5 3 1 34, 35 34 12 6 36,37 22 12 6 38, 39 22 12 6 40, 41 22 12 6 42, 43 22 14 6 44, 45 34 14 1046, 47 34 14 10 48, 49 34 16 9 50, 51 34 16 9 52, 53 34 16 9 54, 55 3415 9 56, 57 34 13 9 58, 59 26 1 8 60, 61 26 1 8 62, 63 26 1 8 64, 65 261 8 66 26 1 8

TABLE 8-X2 Specification of affine linear weighted intra predictioncandidate modes candidate mode 0 1 2 lwipMprnCand[ 0 ] 17 34 5lwipMprnCand[ 1 ] 0 7 16 lwipMprnCand[ 2 ] 1 4 6

8.4.2. Derivation Process for Luma Intra Prediction Mode

Input to this process are:

-   -   a luma location (xCb, yCb) specifying the top-left sample of the        current luma coding block relative to the top-left luma sample        of the current picture,    -   a variable cbWidth specifying the width of the current coding        block in luma samples,    -   a variable cbHeight specifying the height of the current coding        block in luma samples.        In this process, the luma intra prediction mode        IntraPredModeY[xCb][yCb] is derived.        Table 8-1 specifies the value for the intra prediction mode        IntraPredModeY[xCb][yCb] and the associated names.

TABLE 8-1 Specification of intra prediction mode and associated namesIntro prediction mode Associated name 0 INTRA_PLANAR 1 INTRA_DC 2 . . .66 INTRA_ANGULAR2 . . . INTRA_ANGULAR66 81 . . . 83 INTRA_LT_CCLM,INTRA_L_CCLM, INTRA_T_CCLM NOTE-: The intra prediction modesINTRA_LT_CCLM, INTRA_L_CCLM and INTRA_T_CCLM are only applicable tochroma components. IntraPredModeY[ xCb ][[ yCb ] is derived by thefollowing ordered steps:

-   -   1. The neighboring locations (xNbA, yNbA) and (xNbB, yNbB) are        set equal to (xCb−1, yCb+cbHeight−1) and (xCb+cbWidth−1, yCb−1),        respectively.    -   2. For X being replaced by either A or B, the variables        candIntraPredModeX are derived as follows:        -   The availability derivation process for a block as specified            in clause <begin>6.4.X [Ed. (BB): Neighboring blocks            availability checking process tbd]<end> is invoked with the            location (xCurr, yCurr) set equal to (xCb, yCb) and the            neighboring location (xNbY, yNbY) set equal to (xNbX, yNbX)            as inputs, and the output is assigned to availableX.        -   The candidate intra prediction mode candlntraPredModeX is            derived as follows:            -   If one or more of the following conditions are true,                candlntraPredModeX is set equal to INTRA_PLANAR.                -   The variable availableX is equal to FALSE.                -   CuPredMode[xNbX][yNbX] is not equal to MODE_INTRA                    and ciipflag[xNbX][yNbX] is not equal to 1.                -   pcmflag[xNbX][yNbX] is equal to 1.                -   X is equal to B and yCb−1 is less than                    ((yCb>>CtbLog2SizeY)<<CtbLog2SizeY).            -   Otherwise, candlntraPredModeX is derived as follows:                -   If intra_lwipflag[xCb][yCb] is equal to 1,                    candlntraPredModeX is derived by the following                    ordered steps:                -    i. The size type derivation process for a block as                    specified in clause 8.4.X.1 is invoked with the                    width of the current coding block in luma samples                    cbWidth and the height of the current coding block                    in luma samples cbHeight as input, and the output is                    assigned to variable sizeId.                -    ii. candlntraPredModeX is derived using                    IntraPredModeY[xNbX][yNbX] and sizeId as specified                    in Table 8-X3.            -   Otherwise, candlntraPredModeX is set equal to                IntraPredModeY[xNbX][yNbX].    -   3. The variables ispDefaultMode1 and ispDefaultMode2 are defined        as follows:        -   If IntraSubPartitionsSplitType is equal to ISP_HOR_SPLIT,            ispDefaultMode1 is set equal to INTRA_ANGULAR18 and            ispDefaultMode2 is set equal to INTRA_ANGULAR5.        -   Otherwise, ispDefaultMode1 is set equal to INTRA_ANGULAR50            and ispDefaultMode2 is set equal to INTRA_ANGULAR63.            . . .

TABLE 8-X3 Specification of mapping between affine linear weighted intraprediction and intra prediction modes block size type sizeIdIntraPredModeY[ xNbX ][ yNbX ] 0 1 2 0 0 0 1 1 18 1 1 2 18 0 1 3 0 1 1 418 0 18 5 0 22 0 6 12 18 1 7 0 18 0 8 18 1 1 9 2 0 50 10 18 1 0 11 12 012 18 1 13 18 0 14 1 44 15 18 0 16 18 50 17 0 1 18 0 0 19 50 20 0 21 5022 0 23 56 24 0 25 50 26 66 27 50 28 56 29 50 30 50 31 1 32 50 33 50 3450

8.4.3 Derivation Process for Chroma Intra Prediction Mode

Input to this process are:

-   -   a luma location (xCb, yCb) specifying the top-left sample of the        current chroma coding block relative to the top-left luma sample        of the current picture,    -   a variable cbWidth specifying the width of the current coding        block in luma samples,    -   a variable cbHeight specifying the height of the current coding        block in luma samples.        In this process, the chroma intra prediction mode        IntraPredModeC[xCb][yCb] is derived.        The corresponding luma intra prediction mode lumalntraPredMode        is derived as follows:    -   If intra_lwip_flag[xCb][yCb] is equal to 1, lumalntraPredMode is        derived by the following ordered steps:        -   i. The size type derivation process for a block as specified            in clause 8.4.X.1 is invoked with the width of the current            coding block in luma samples cbWidth and the height of the            current coding block in luma samples cbHeight as input, and            the output is assigned to variable sizeId.        -   ii. The luma intra prediction mode is derived using            IntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2] and sizeId as            specified in Table 8-X3 and assigning the value of            candlntraPredModeX to lumalntraPredMode.    -   Otherwise, lumalntraPredMode is set equal to        IntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2].        The chroma intra prediction mode IntraPredModeC[xCb][yCb] is        derived using intra_chroma_pred_mode[xCb][yCb] and        lumalntraPredMode as specified in Table 8-2 and Table 8-3.        . . .        xxx. Intra Sample Prediction

<Begin>

Inputs to this process are:

-   -   a sample location (xTbCmp, yTbCmp) specifying the top-left        sample of the current transform block relative to the top-left        sample of the current picture,    -   a variable predModeIntra specifying the intra prediction mode,    -   a variable nTbW specifying the transform block width,    -   a variable nTbH specifying the transform block height,    -   a variable nCbW specifying the coding block width,    -   a variable nCbH specifying the coding block height,    -   a variable cldx specifying the colour component of the current        block.        Outputs of this process are the predicted samples        predSamples[x][y], with x=0 . . . nTbW−1, y=0 . . . nTbH−1.        The predicted samples predSamples[x][y] are derived as follows:    -   If intra_lwip_flag[xTbCmp][yTbCmp] is equal to 1 and cldx is        equal to 0, the affine linear weighted intra sample prediction        process as specified in clause 8.4.4.2.X1 is invoked with the        location (xTbCmp, yTbCmp), the intra prediction mode        predModeIntra, the transform block width nTbW and height nTbH as        inputs, and the output is predSamples.    -   Otherwise, the general intra sample prediction process as        specified in clause 8.4.4.2.X1. is invoked with the location        (xTbCmp, yTbCmp), the intra prediction mode predModeIntra, the        transform block width nTbW and height nTbH, the coding block        width nCbW and height nCbH, and the variable cldx as inputs, and        the output is predSamples.

8.4.4.2.X1 Affine Linear Weighted Intra Sample Prediction

Inputs to this process are:

-   -   a sample location (xTbCmp, yTbCmp) specifying the top-left        sample of the current transform block relative to the top-left        sample of the current picture,    -   a variable predModeIntra specifying the intra prediction mode,    -   a variable nTbW specifying the transform block width,    -   a variable nTbH specifying the transform block height.

Outputs of this process are the predicted samples predSamples[x][y],with x=0 . . . nTbW−1, y=0 . . . nTbH−1.

The size type derivation process for a block as specified in clause8.4.X.1 is invoked with the transform block width nTbW and the transformblock height nTbH as input, and the output is assigned to variablesizeId.Variables numModes, boundarySize, predW, predH and predC are derivedusing sizeId as specified in Table 8-X4.

TABLE 8-X4 Specification of number of modes, boundary sample size andprediction sizes depending on sizeId sizeId numModes boundarySize predWpredH predC 0 35 2 4 4 4 1 19 4 4 4 4 2 11 4 Min( nTbW, 8 ) Min( nTbH, 8) 8The flag isTransposed is derived as follows:

isTransposed=(predModeIntra>(numModes/2))?1:0  (8-X15)

The flags needUpsBdryHor and needUpsBdryVer are derived as follows:

needUpsBdryHor=(nTbW>predW)?TRUE: FALSE  (8-X16)

needUpsBdryVer=(nTbH>predH)?TRUE:FALSE  (8-X17)

The variables upsBdryW and upsBdryH are derived as follows:

upsBdryW=(nTbH>nTbW)?nTbW:predW  (8-X18)

upsBdryH=(nTbH>nTbW)?predH: nTbH  (8-X19)

The variables lwipW and lwipH are derived as follows:

lwipW=(isTransposed==1)?predH:predW  (8-X20)

lwipH=(isTransposed==1)?predW:predH  (8-X21)

For the generation of the reference samples refT[x] with x=0 . . .nTbW−1 and refL[y] with y=0 . . . nTbH−1, the reference samplederivation process as specified in clause 8.4.4.2.X2 is invoked with thesample location (xTbCmp, yTbCmp), the transform block width nTbW, thetransform block height nTbH as inputs, and top and left referencesamples refT[x] with x=0 . . . nTbW−1 and refL[y] with y=0 . . . nTbH−1,respectively, as outputs.For the generation of the boundary samples p[x] withx=0..2*boundarySize−1, the following applies:

-   -   The boundary reduction process as specified in clause 8.4.4.2.X3        is invoked for the top reference samples with the block size        nTbW, the reference samples refT, the boundary size        boundarySize, the upsampling boundary flag needUpsBdryVer, and        the upsampling boundary size upsBdryW as inputs, and reduced        boundary samples redT[x] with x=0 . . . boundarySize−1 and        upsampling boundary samples upsBdryT[x] with x=0 . . .        upsBdryW−1 as outputs.    -   The boundary reduction process as specified in clause 8.4.4.2.X3        is invoked for the left reference samples with the block size        nTbH, the reference samples refL, the boundary size        boundarySize, the upsampling boundary flag needUpsBdryHor, and        the upsampling boundary size upsBdryH as inputs, and reduced        boundary samples redL[x] with x=0 . . . boundarySize−1 and        upsampling boundary samples upsBdryL[x] with x=0 . . .        upsBdryH−1 as outputs.    -   The reduced top and left boundary samples redT and redL are        assigned to the boundary sample array p as follows:    -   If isTransposed is equal to 1, p[x] is set equal to redL[x] with        x=0 . . . boundarySize−1 and p[x+boundarySize] is set equal to        redT[x] with x=0 . . . boundarySize−1.    -   Otherwise, p[x] is set equal to redT[x] with x=0 . . .        boundarySize−1 and p[x+boundarySize] is set equal to redL[x]        with x=0 . . . boundarySize−1.        For the intra sample prediction process according to        predModeIntra, the following ordered steps apply:    -   1. The affine linear weighted samples predLwip[x][y], with x=0 .        . . lwipW−1, y=0 . . . lwipH−1 are derived as follows:        -   The variable modeId is derived as follows:

modeId=predModeIntra−(isTransposed==1)?(numModes/2):0  (8-X22)

-   -   -   The weight matrix mWeight[x][y] with x=0 . . .            2*boundarySize−1, y=0 . . . predC*predC−1 is derived using            sizeId and modeId as specified in Table 8-XX [TBD: add            weight matrices].

    -   The bias vector vBias[y] with y=0 . . . predC*predC−1 is derived        using sizeId and modeId as specified in Table 8-XX [TBD: add        bias vectors].

    -   The variable sW is derived using sizeId and modeId as specified        in Table 8-X5.

    -   The affine linear weighted samples predLwip[x][y], with x=0 . .        . lwipW−1, y=0 . . . lwipH−1 are derived as follows:

oW=1<<(sW−1)  (8-X23)

sB=BitDepth_(Y)−1  (8-X24)

incW=(predC>lwipW)?2:1  (8-X25)

incH=(predC>lwipH)?2:1  (8-X26)

predLwip[x][y]=((Σ_(i=0)^(2*boundarySize-1)mWeight[i][y*incH*predC+x*incW]*p[i])+(vBias[y*incH*predC+x*incW]<<sB)+oW)>>sW  (8-X27)

-   -   2. The predicted samples predSamples[x][y], with x=0 . . .        nTbW−1, y=0 . . . nTbH−1 are derived as follows:        -   When isTransposed is equal to 1, predLwip[x][y], with x=0 .            . . predW−1, y=0 . . . predH−1 is set equal to            predLwip[y][x].        -   If needUpsBdryVer is equal to TRUE or needUpsBdryHor is            equal to TRUE, the prediction upsampling process as            specified in clause 8.4.4.2.X4 is invoked with the input            block width predW, the input block height predH, affine            linear weighted samples predLwip, the transform block width            nTbW, the transform block height nTbH, the upsampling            boundary width upsBdryW, the upsampling boundary height            upsBdryH, the top upsampling boundary samples upsBdryT, and            the left upsampling boundary samples upsBdryL as inputs, and            the output is the predicted sample array predSamples.        -   Otherwise, predSamples[x][y], with x=0 . . . nTbW−1, y=0 . .            . nTbH−1 is set equal to predLwip[x][y].

TABLE 8-X5 Specification of weight shifts sW depending on sizeId andmodeId modeId sizeId 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 0 8 8 88 8 8 8 8 8 8 8 8 8 8 8 8 8 8 1 8 8 8 9 8 8 8 8 9 8 2 8 8 8 8 8 8

8.4.4.2.X2 Reference Sample Derivation Process

Inputs to this process are:

-   -   a sample location (xTbY, yTbY) specifying the top-left luma        sample of the current transform block relative to the top-left        luma sample of the current picture,    -   a variable nTbW specifying the transform block width,    -   a variable nTbH specifying the transform block height.        Outputs of this process are the top and left reference samples        refT[x] with x=0 . . . nTbW−1 and refL[y] with y=0 . . . nTbH−1,        respectively.        The neighboring samples refT[x] with x=0 . . . nTbW−1 and        refL[y] with y=0 . . . nTbH−1 are constructed samples prior to        the in-loop filter process and derived as follows:    -   The top and left neighboring luma locations (xNbT, yNbT) and        (xNbL, yNbL) are specified by:

(xNbT,yNbT)=(xTbY+x,yTbY−1)   (8-X28)

(xNbL,yNbL)=(xTbY−1,yTbY+y)   (8-X29)

-   -   The availability derivation process for a block as specified in        clause 6.4.X [Ed. (BB): Neighboring blocks availability checking        process tbd] is invoked with the current luma location (xCurr,        yCurr) set equal to (xTbY, yTbY) and the top neighboring luma        location (xNbT, yNbT) as inputs, and the output is assigned to        availTop[x] with x=0 . . . nTbW−1.    -   The availability derivation process for a block as specified in        clause 6.4.X [Ed. (BB): Neighboring blocks availability checking        process tbd] is invoked with the current luma location (xCurr,        yCurr) set equal to (xTbY, yTbY) and the left neighboring luma        location (xNbL, yNbL) as inputs, and the output is assigned to        availLeft[y] with y=0 . . . nTbH−1.    -   The top reference samples refT[x] with x=0 . . . nTbW−1 are        derived as follows:        -   If all availTop[x] with x=0 . . . nTbW−1 are equal to TRUE,            the sample at the location (xNbT, yNbT) is assigned to            refT[x] with x=0 . . . nTbW−1.        -   Otherwise, if availTop[0] is equal to FALSE, all refT[x]            with x=0 . . . nTbW−1 are set equal to 1<<(BitDepth_(Y)−1).        -   Otherwise, reference samples refT[x] with x=0 . . . nTbW−1            are derived by the following ordered steps:            -   1. The variable lastT is set equal to the position x of                the first element in the sequence availTop[x] with x=1 .                . . nTbW−1 that is equal to FALSE.            -   2. For every x=0 . . . lastT−1, the sample at the                location (xNbT, yNbT) is assigned to refT[x].            -   3. For every x=lastT . . . nTbW−1, refT[x] is set equal                to refT[lastT−1].    -   The left reference samples refL[y] with x=0 . . . nTbH−1 are        derived as follows:        -   If all availLeft[y] with y=0 . . . nTbH−1 are equal to TRUE,            the sample at the location (xNbL, yNbL) is assigned to            refL[y] with y=0 . . . nTbH−1.        -   Otherwise, if availLeft[0] is equal to FALSE, all refL[y]            with y=0 . . . nTbH−1 are set equal to 1<<(BitDepth_(Y)−1).        -   Otherwise, reference samples refL[y] with y=0 . . . nTbH−1            are derived by the following ordered steps:            -   1. The variable lastL is set equal to the position y of                the first element in the sequence availLeft[y] with y=1                . . . nTbH−1 that is equal to FALSE.            -   2. For every y=0 . . . lastL−1, the sample at the                location (xNbL, yNbL) is assigned to refL[y].            -   3. For every y=lastL . . . nTbH−1, refL[y] is set equal                to refL[lastL−1].

Specification of the Boundary Reduction Process

Inputs to this process are:

-   -   a variable nTbX specifying the transform block size,    -   reference samples refX[x] with x=0 . . . nTbX−1,    -   a variable boundarySize specifying the downsampled boundary        size,    -   a flag needUpsBdryX specifying whether intermediate boundary        samples are required for upsampling,    -   a variable upsBdrySize specifying the boundary size for        upsampling.        Outputs of this process are the reduced boundary samples redX[x]        with x=0 . . . boundarySize−1 and upsampling boundary samples        upsBdryX[x] with x=0 . . . upsBdrySize−1.        The upsampling boundary samples upsBdryX[x] with x=0 . . .        upsBdrySize−1 are derived as follows:    -   If needUpsBdryX is equal to TRUE and upsBdrySize is less than        nTbX, the following applies:

uDwn=nTbX/upsBdrySize  (8-X30)

upsBdryX[x]=(Σ_(i=0) ^(uDwn-1) refX[x*uDwn+i]+(1<<(Log 2(uDwn)−1)))>>Log2(uDwn)  (8-X31)

-   -   Otherwise (upsBdrySize is equal to nTbX), upsBdryX[x] is set        equal to refX[x].        The reduced boundary samples redX[x] with x=0 . . .        boundarySize−1 are derived as follows:    -   If boundarySize is less than upsBdrySize, the following applies:

bDwn=upsBdrySize/boundarySize  (8-X32)

redX[x]=(Σ_(i=0) ^(bDwn-1)upsBdryX[x*bDwn+i]+(1<<(Log 2(bDwn)−1)))>>Log2(bDwn)  (8-X33)

-   -   Otherwise (boundarySize is equal to upsBdrySize), redX[x] is set        equal to upsBdryX[x].

8.4.4.2.X4 Specification of the Prediction Upsampling Process

Inputs to this process are:

-   -   a variable predW specifying the input block width,    -   a variable predH specifying the input block height,    -   affine linear weighted samples predLwip[x][y], with x=0 . . .        predW−1, y=0 . . . predH−1,    -   a variable nTbW specifying the transform block width,    -   a variable nTbH specifying the transform block height,    -   a variable upsBdryW specifying the upsampling boundary width,    -   a variable upsBdryH specifying the upsampling boundary height,    -   top upsampling boundary samples upsBdryT[x] with x=0 . . .        upsBdryW−1,    -   left upsampling boundary samples upsBdryL[x] with x=0 . . .        upsBdryH−1.        Outputs of this process are the predicted samples        predSamples[x][y], with x=0 . . . nTbW−1, y=0 . . . nTbH−1.        The sparse predicted samples predSamples[m][n] are derived from        predLwip[x][y], with x=0 . . . predW−1, y=0 . . . predH−1 as        follows:

upHor=nTbW/predW  (8-X34)

upVer=nTbH/predH  (8-X35)

predSamples[(x+1)*upHor−1][(y+1)*upVer−1]=predLwip[x][y]  (8-X36)

The top boundary samples upsBdryT[x] with x=0 . . . upsBdryW−1 areassigned to predSamples[m][−1] as follows:

predSamples[(x+1)*(nTbW/upsBdryW)−1][−1]=upsBdryT[x]  (8-X37)

The left boundary samples upsBdryL[y] with y=0 . . . upsBdryH−1 areassigned to predSamples[−1][n] as follows:

predSamples[−1][(y+1)*(nTbH/upsBdryH)−1]=upsBdryL[y]  (8-X38)

The predicted samples predSamples[x][y], with x=0 . . . nTbW−1, y=0 . .. nTbH−1 are derived as follows:

-   -   If nTbH is greater than nTbW, the following ordered steps apply:        -   1. When upHor is greater than 1, horizontal upsampling for            all sparse positions (xHor, yHor)=(m*upHor−1, n*upVer−1)            with m=0 . . . predW−1, n=1 . . . predH is applied with dX=1            . . . upHor−1 as follows:

predSamples[xHor+dX][yHor]=((upHor−dX)*predSamples[xHor][yHor]+dX*predSamples[xHor+upHor][yHor])/upHor  (8-X39)

-   -   -   2. Vertical upsampling for all sparse positions (xVer, yVer)            (im, n*upVer−1) with m=0 . . . nTbW−1, n=0 . . . predH−1 is            applied with dY=1 . . . upVer−1 as follows:

predSamples[xVer][yVer+dY]=((upVer−dY)*predSamples[xVer][yVer]+dY*predSamples[xVer][yVer+upVer])/upVer  (8-X40)

-   -   Otherwise, the following ordered steps apply:        -   1. When upVer is greater than 1, vertical upsampling for all            sparse positions (xVer, yVer)=(m*upHor−1, n*upVer−1) with            m=1 . . . predW, n=0 . . . predH−1 is applied with dY=1 . .            . upVer−1 as specified in (8-X40).        -   2. Horizontal upsampling for all sparse positions (xHor,            yHor) (m*upHor−1, n) with m=0 . . . predW−1, n=0 . . .            nTbH−1 is applied with dX=1 . . . upHor−1 as specified in            (8-X39).

<End>

TABLE 9-9 Syntax elements and associated binarizations BinarizationSyntax structure Syntax element Process Input parameters coding_unit( )cu_skip_flag[ ][ ] FL cMax = 1 pred_mode_ibc_flag FL cMax = 1pred_mode_flag FL cMax = 1 <begin>intra_lwip_flag[ ][ ] FL cMax = 1intra_lwip_mpm_flag[ ][ ] FL cMax = 1 intra_lwip_mpm_idx[ ][ ] TR cMax =2, cRiceParam = 0 intra_lwip_mpm_remainder [ ][ ] FL cMax = (cbWidth = =4 && cbHeight = = 4) ? 31 : ( (cbWidth <= 8 && cbHeight <= 8) ? 15: 7) .. .

TABLE 9-15 Assignment of ctxInc to syntax elements with context codedbins Syntax binIdx element 0 1 2 3 4 >= 5 . . . terminate na na na na na

TABLE 9-15 Assignment of ctxInc to syntax elements with context codedbins binIdx Syntax element 0 1 2 3 4 >= 5 intra_lwip_flag[ ][ ] (Abs(Log2 na na na na na (cbWidth) − Log2(cbHeight) ) > 1) ? 3 : ( 0,1,2(clause 9.5.4.2.2) ) intra_lwip_mpm_flag 0 na na na na na [ ][ ]intra_lwip_mpm_idx bypass bypass na na na na [ ][ ] intra_lwip_mpm_bypass bypass bypass bypass bypass na remainder[ ][ ]

TABLE 9-16 Specification of ctxInc using left and above syntax elementsSyntax element condL condA ctxSetIdx . . . intra_lwip_flag[ x0 ] [ y0 ]intra_lwip_flag[ xNbL ][ yNbL ] intra_lwip_flag[ xNbA ][ yNbA ] 0 . . .<end>

Summary of ALWIP

For predicting the samples of a rectangular block of width W and heightH, affine linear weighted intra prediction (ALWIP) takes one line of Hreconstructed neighboring boundary samples left of the block and oneline of W reconstructed neighboring boundary samples above the block asinput. If the reconstructed samples are unavailable, they are generatedas it is done in the conventional intra prediction. ALWIP is onlyapplied to luma intra block. For chroma intra block, the conventionalintra coding modes are applied.

The generation of the prediction signal is based on the following threesteps:

-   -   1. Out of the boundary samples, four samples in the case of        W=H=4 and eight samples in all other cases are extracted by        averaging.    -   2. A matrix vector multiplication, followed by addition of an        offset, is carried out with the averaged samples as an input.        The result is a reduced prediction signal on a subsampled set of        samples in the original block.    -   3. The prediction signal at the remaining positions is generated        from the prediction signal on the subsampled set by linear        interpolation which is a single step linear interpolation in        each direction.

If an ALWIP mode is to be applied, the index predmode of the ALWIP modeis signaled using a MPM-list with 3 MPMS. Here, the derivation of theMPMs is performed using the intra-modes of the above and the left PU asfollows. There are three fixed tables map_angular_to_alwip_(idx),idx∈{0,1,2} that assign to each conventional intra prediction modepredmode_(Angular) an ALWIP mode

predmode_(ALWIP)=map_angular_to_alwip_(idx)[predmode_(Angular)].

For each PU of width W and height H one defines an index

idx(PU)=idx(W,H)∈{0,1,2}

that indicates from which of the three sets the ALWIP-parameters are tobe taken.

If the above Prediction Unit PU_(above) is available, belongs to thesame CTU as the current PU and is in intra mode, ifidx(PU)=idx(PU_(above)) and if ALWIP is applied on PU_(above) withALWIP-mode predmode_(ALWIP) ^(above), one puts

mode_(ALWIP) ^(above)=predmode_(ALWIP) ^(above).

If the above PU is available, belongs to the same CTU as the current PUand is in intra mode and if a conventional intra prediction modepredmode_(Angular) ^(above) is applied on the above PU, one puts

mode_(ALWIP) ^(above)=map_angular_to_alwip_(idx(PU) _(above)₎[predmode_(Angular) ^(above)].

In all other cases, one puts

mode_(ALWIP) ^(above)=−1

which means that this mode is unavailable. In the same way but withoutthe restriction that the left PU needs to belong to the same CTU as thecurrent PU, one derives a mode mode_(ALWIP) ^(left).

Finally, three fixed default lists list_(idx), idx∈{0,1,2} are provided,each of which contains three distinct ALWIP modes. Out of the defaultlist list_(idx(PU)) and the modes mode_(ALWIP) ^(above) andmode_(ALWIP), one constructs three distinct MPMs by substituting −1 bydefault values as well as eliminating repetitions.

For the luma MPM-list derivation, whenever a neighboring luma block isencountered which uses an ALWIP-mode predmode_(ALWIP), this block istreated as if it was using the conventional intra-prediction modepredmode_(Angular).

predmode_(Angular)=map_alwip_to_angular_(idx(PU))[predmode_(ALWIP)]

3 Transform in VVC 3.1 Multiple Transform Selection (MTS)

In addition to DCT-II which has been employed in HEVC, a MultipleTransform Selection (MTS) scheme is used for residual coding both interand intra coded blocks. It uses multiple selected transforms from theDCT8/DST7. The newly introduced transform matrices are DST-VII andDCT-VIII.

3.2 Reduced Secondary Transform (RST) Proposed in JVET-N0193

Reduced secondary transform (RST) applies 16×16 and 16×64 non-separabletransform for 4×4 and 8×8 blocks, respectively. Primary forward andinverse transforms are still performed the same way as two 1-Dhorizontal/vertical transform passes. Secondary forward and inversetransforms are a separate process step from that of primary transforms.For encoder, primary forward transform is performed first, then followedby secondary forward transform and quantization, and CABAC bit encoding.For decoder, CABAC bit decoding and inverse quantization, then Secondaryinverse transform is performed first, then followed by primary inversetransform. RST applies only to intra coded TUs in both intra slice andinter slices.

3.3 a Unified MPM List for Intra Mode Coding in JVET-N0185

A unified 6-MPM list is proposed for intra blocks irrespective ofwhether Multiple Reference Line (MRL) and Intra sub-partition (ISP)coding tools are applied or not. The MPM list is constructed based onintra modes of the left and above neighboring block as in VTM4.0.Suppose the mode of the left is denoted as Left and the mode of theabove block is denoted as Above, the unified MPM list is constructed asfollows:

-   -   When a neighboring block is not available, its intra mode is set        to Planar by default.    -   If both modes Left and Above are non-angular modes:    -   a. MPM list→{Planar, DC, V, H, V−4, V+4}    -   If one of modes Left and Above is angular mode, and the other is        non-angular:    -   a. Set a mode Max as the larger mode in Left and Above    -   b. MPM list→{Planar, Max, DC, Max−1, Max+1, Max−2}    -   If Left and Above are both angular and they are different:    -   a. Set a mode Max as the larger mode in Left and Above    -   b. if the difference of mode Left and Above is in the range of 2        to 62, inclusive        -   i. MPM list→{Planar, Left, Above, DC, Max−1, Max+1}    -   c. Otherwise        -   i. MPM list→{Planar, Left, Above, DC, Max−2, Max+2}    -   If Left and Above are both angular and they are the same:    -   a. MPM list→{Planar, Left, Left−1, Left+1, DC, Left−2}

Besides, the first bin of the MPM index codeword is CABAC context coded.In total three contexts are used, corresponding to whether the currentintra block is MRL enabled, ISP enabled, or a normal intra block.

The left neighboring block and above neighboring block used in theunified MPM list construction is A2 and B2 as shown in FIG. 10.

One MPM flag is firstly coded. If the block is coded with one of mode inthe MPM list, an MPM index is further coded. Otherwise, an index to theremaining modes (excluding MPMs) is coded.

4 Examples of Drawbacks in Existing Implementations

The design of ALWIP in JVET-N0217 has the following problems:

-   -   1) At the March 2019 JVET meeting, a unified 6-MPM list        generation was adopted for MRL mode, ISP mode, and normal intra        mode. But the affine linear weighted prediction mode uses a        different 3-MPM list construction which makes the MPM list        construction complicated. A complex MPM list construction might        compromise the throughput of the decoder, in particular for        small blocks such as 4×4 samples.    -   2) ALWIP is only applied to luma component of the block. For the        chroma component of an ALWP coded block, a chroma mode index is        coded and sent to decoder, which could result in unnecessary        signaling.    -   3) The interactions of ALWIP with other coding tools should be        considered.    -   4) When calculating upsBdryX in upsBdryX[x]=(Σ_(i=0)        ^(uDwn-1)refX[x*uDwn+i]+(1<<(Log 2(uDwn)−1)))>>Log 2(uDwn)        (8-X31), it is possible that Log 2(uDwn)−1 is equal to −1, while        left shifted with −1 is undefined.    -   5) When upsampling the prediction samples, no rounding is        applied.    -   6) In the deblocking process, ALWIP coded blocks are treated as        normal intra-blocks.

5 Exemplary Methods for Matrix-Based Intra Coding

Embodiments of the presently disclosed technology overcome drawbacks ofexisting implementations, thereby providing video coding with highercoding efficiencies but lower computational complexity. Matrix-basedintra prediction methods for video coding, and as described in thepresent document, may enhance both existing and future video codingstandards, is elucidated in the following examples described for variousimplementations. The examples of the disclosed technology provided belowexplain general concepts, and are not meant to be interpreted aslimiting. In an example, unless explicitly indicated to the contrary,the various features described in these examples may be combined.

In the following discussion, an intra-prediction mode refers to anangular intra prediction mode (including DC, planar, CCLM and otherpossible intra prediction modes); while an intra mode refers to normalintra mode, or MRL, or ISP or ALWIP.

In the following discussion, “Other intra modes” may refer to one ormultiple intra modes except ALWIP, such as normal intra mode, or MRL, orISP.

In the following discussion, SatShift(x, n) is defined as

${{SatShift}\left( {x,n} \right)} = \left\{ \begin{matrix}{{\left( {x + {{offset}\; 0}} \right)\mspace{14mu}\text{>>}\mspace{14mu} n\mspace{14mu}{if}\mspace{14mu} x} \geq 0} \\{{{- \left( {\left( {{- x} + {{offset}\; 1}} \right)\mspace{14mu}\text{>>}\mspace{14mu} n} \right)}\mspace{14mu}{if}\mspace{14mu} x} < 0}\end{matrix} \right.$

Shift(x, n) is defined as Shift(x, n)=(x+offset0)>>n.

In one example, offset0 and/or offset1 are set to (1<<n)>>1 or(1<<(n−1)). In another example, offset0 and/or offset1 are set to 0.

In another example, offset0=offset1=((1<<n)>>1)−1 or ((1<<(n−1)))−1.

Clip3(min, max, x) is defined as

${{Clip}\; 3\left( {{Min},{Max},x} \right)} = \left\{ \begin{matrix}{Min} & {{{if}\mspace{14mu} x} < {Min}} \\{Max} & {{{if}\mspace{14mu} x} > {Max}} \\x & {Otherwise}\end{matrix} \right.$

MPM List Construction for ALWIP

-   -   1. It is proposed that the whole or partial of the MPM list for        ALWIP may be constructed according to the whole or partial        procedure to construct the MPM list for non-ALWIP intra mode        (such as normal intra mode, MRL, or ISP).        -   a. In one example, the size of the MPM list for ALWIP may be            the same as that of the MPM list for non-ALWIP intra mode.            -   i. For example, the size of MPM list is 6 for both ALWIP                and non-ALWIP intra modes.        -   b. In one example, the MPM list for ALWIP may be derived            from the MPM list for non-ALWIP intra mode.            -   i. In one example, the MPM list for non-ALWIP intra mode                may be firstly constructed. Afterwards, partial or all                of them may be converted to the MPMs which may be                further added to the MPM list for ALWIP coded blocks.                -   1) Alternatively, furthermore, when adding a                    converted MPM to the MPM list for ALWIP coded                    blocks, pruning may be applied.                -   2) Default modes may be added to the MPM list for                    ALWIP coded blocks.                -    a. In one example, default modes may be added                    before those converted from the MPM list of                    non-ALWIP intra mode.                -    b. Alternatively, default modes may be added after                    those converted from the MPM list of non-ALWIP intra                    mode.                -    c. Alternatively, default modes may be added in an                    interleaved way with those converted from the MPM                    list of non-ALWIP intra mode.                -    d. In one example, the default modes may be fixed                    to be the same for all kinds of blocks.                -    e. Alternatively, the default modes may be                    determined according to coded information, such as                    availability of neighboring blocks, mode information                    of neighboring blocks, block dimension.            -   ii. In one example, one intra-prediction mode in the MPM                list for non-ALWIP intra mode may be converted to its                corresponding ALWIP intra-prediction mode, when it is                put into the MPM list for ALWIP.                -   1) Alternatively, all the intra-prediction modes in                    the MPM list for non-ALWIP intra modes may be                    converted to corresponding ALWIP intra-prediction                    modes before being used to construct the MPM list                    for ALWIP.                -   2) Alternatively, all the candidate intra-prediction                    modes (may include the intra-prediction modes from                    neighboring blocks and default intra-prediction                    modes such as Planar and DC) may be converted to                    corresponding ALWIP intra-prediction modes before                    being used to construct the MPM list for non-ALWIP                    intra modes, if the MPM list for non-ALWIP intra                    modes may be further used to derive the MPM list for                    ALWIP.                -   3) In one example, two converted ALWIP                    intra-prediction modes may be compared.                -    a. In one example, if they are the same, only one                    of them may be put into the MPM list for ALWIP.                -    b. In one example, if they are the same, only one                    of them may be put into the MPM list for non-ALWIP                    intra modes.            -   iii. In one example, K out of S intra-prediction modes                in the MPM list for non-ALWIP intra modes may be picked                as the MPM list for ALWIP mode. E.g., K is equal to 3                and S is equal to 6.                -   1) In one example, the first K intra-prediction                    modes in the MPM list for non-ALWIP intra modes may                    be picked as the MPM list for ALWIP mode.    -   2. It is proposed that the one or multiple neighboring blocks        used to derive the MPM list for ALWIP may also be used to used        derive the MPM list for non-ALWIP intra modes (such as normal        intra mode, MRL, or ISP).        -   a. In one example, the neighboring block left to the current            block used to derive the MPM list for ALWIP should be the            same as that used to derive the MPM list for non-ALWIP intra            modes.            -   i. Suppose the top-left corner of the current block is                (xCb, yCb), the width and height of the current block                are W and H, then in one example, the left neighboring                block used to derive the MPM list for both ALWIP and                non-ALWIP intra modes may cover the position (xCb−1,                yCb). In an alternative example, the left neighboring                block used to derive the MPM list for both ALWIP and                non-ALWIP intra modes may cover the position (xCb−1,                yCb+H−1).            -   ii. For example, the left neighboring block and above                neighboring block used in the unified MPM list                construction is A2 and B2 as shown in FIG. 10.        -   b. In one example, the neighboring block above to the            current block used to derive the MPM list for ALWIP should            be the same as that used to derive the MPM list for            non-ALWIP intra modes.            -   i. Suppose the top-left corner of the current block is                (xCb, yCb), the width and height of the current block                are W and H, then in one example, the above neighboring                block used to derive the MPM list for both ALWIP and                non-ALWIP intra modes may cover the position (xCb,                yCb−1). In an alternative example, the above neighboring                block used to derive the MPM list for both ALWIP and                non-ALWIP intra modes may cover the position (xCb+W−1,                yCb−1).            -   ii. For example, the left neighboring block and above                neighboring block used in the unified MPM list                construction is A1 and B1 as shown in FIG. 10.    -   3. It is proposed that the MPM list for ALWIP may be constructed        in different ways according to the width and/or height of the        current block.        -   a. In one example, different neighboring blocks may be            accessed for different block dimensions.    -   4. It is proposed that the MPM list for ALWIP and the MPM list        for non-ALWIP intra modes may be constructed with the same        procedure but with different parameters.        -   a. In one example, K out of S intra-prediction modes in the            MPM list construction procedure of non-ALWIP intra modes may            be derived for the MPM list used in ALWIP mode. E.g., K is            equal to 3 and S is equal to 6.            -   i. In one example, the first K intra-prediction modes in                the MPM list construction procedure may be derived for                the MPM list used in ALWIP mode.        -   b. In one example, the first mode in the MPM list may be            different.            -   i. For example, the first mode in the MPM list for                non-ALWIP intra modes may be Planar, but it may be a                Mode X0 in the MPM list for ALWIP.                -   1) In one example, X0 may be the ALWIP                    intra-prediction mode converted from Planar.        -   c. In one example, stuffing modes in the MPM list may be            different.            -   i. For example, the first three stuffing modes in the                MPM list for non-ALWIP intra modes may be DC, Vertical                and Horizontal, but they may be Mode X1, X2, X3 in the                MPM list for ALWIP.                -   1) In one example, X1, X2, X3 may be different for                    different sizeId.            -   ii. In one example, the number of stuffing mode may be                different.        -   d. In one example, neighboring modes in the MPM list may be            different.            -   i. For example, the normal intra-prediction modes of                neighboring blocks are used to construct the MPM list                for non-ALWIP intra modes. And they are converted to                ALWIP intra-prediction modes to construct the MPM list                for ALWIP mode.        -   e. In one example, the shifted modes in the MPM list may be            different.            -   i. For example, X+K0 where X is a normal                intra-prediction mode and K0 is an integer may be put                into the MPM list for non-ALWIP intra modes. And Y+K1                where Y is an ALWIP intra-prediction mode and K1 is an                integer may be put into the MPM list for ALWIP, where K0                may be different from K1.                -   1) In one example, K1 may depend on the width and                    height.    -   5. It is proposed that a neighboring block is treated as        unavailable if it is coded with ALWIP when constructing the MPM        list for the current block with non-ALWIP intra modes.        -   a. Alternatively, a neighboring block is treated as being            coded with a predefined intra-prediction mode (such as            Planar) if it is coded with ALWIP when constructing the MPM            list for the current block with non-ALWIP intra modes.    -   6. It is proposed that a neighboring block is treated as        unavailable if it is coded with non-ALWIP intra modes when        constructing the MPM list for the current block with ALWIP mode.        -   a. Alternatively, a neighboring block is treated as being            coded with a predefined ALWIP intra-prediction mode X if it            is coded with non-ALWIP intra modes when constructing the            MPM list for the current block with ALWIP mode.            -   i. In one example, X may depend on the block dimensions,                such as width and/or height.    -   7. It is proposed to remove the storage of ALWIP flag from line        buffer.        -   a. In one example, when the 2^(nd) block to be accessed is            located in a different LCU/CTU row/region compared to the            current block, the conditional check of whether the 2^(nd)            block is coded with ALWIP is skipped.        -   b. In one example, when the 2^(nd) block to be accessed is            located in a different LCU/CTU row/region compared to the            current block, the 2^(nd) block is treated in the same way            as non-ALWIP mode, such as treated as normal intra coded            block.    -   8. When encoding the ALWIP flag, no more than K (K>=0) contexts        may be used. a. In one example, K=1.    -   9. It is proposed to store the converted intra prediction mode        of ALWIP coded blocks instead of directly storing the mode index        associated with the ALWIP mode.        -   a. In one example, the decoded mode index associated with            one ALWIP coded block is mapped to the normal intra mode,            such as according to map_alwip_to_angular as described in            Section 2.5.7.        -   b. Alternatively, furthermore, the storage of ALWIP flag is            totally removed.        -   c. Alternatively, furthermore, the storage of ALWIP mode is            totally removed.        -   d. Alternatively, furthermore, condition check of whether            one neighboring/current block is coded with ALWIP flag may            be skipped.        -   e. Alternatively, furthermore, the conversion of modes            assigned for ALWIP coded blocks and normal intra predictions            associated with one accessed block may be skipped.

ALWIP on Different Color Components

-   -   10. It is proposed that an inferred chroma intra mode (e.g., DM        mode) might be always applied if the corresponding luma block is        coded with ALWIP mode.        -   a. In one example, chroma intra mode is inferred to be DM            mode without signaling if the corresponding luma block is            coded with ALWIP mode.        -   b. In one example, the corresponding luma block may be the            one covering the corresponding sample of a chroma sample            located at a given position (e.g., top-left of current            chroma block, center of current chroma block).        -   c. In one example, the DM mode may be derived according to            the intra prediction mode of the corresponding luma block,            such as via mapping the (ALWIP) mode to one of the normal            intra mode.    -   11. When the corresponding luma block of the chroma blocks is        coded with ALWIP mode, several DM modes may be derived.    -   12. It is proposed that a special mode is assigned to the chroma        blocks if one corresponding luma block is coded with ALWIP mode.        -   a. In one example, the special mode is defined to be a given            normal intra prediction mode regardless the intra prediction            mode associated with the ALWIP coded blocks.        -   b. In one example, different ways of intra prediction may be            assigned to this special mode.    -   13. It is proposed that ALWIP may also be applied to chroma        components.        -   a. In one example, the matrix and/or bias vector may be            different for different color components.        -   b. In one example, the matrix and/or bias vector may be            predefined jointly for Cb and Cr.            -   i. In one example, Cb and Cr component may be                concatenated.            -   ii. In one example, Cb and Cr component may be                interleaved.        -   c. In one example, the chroma component may share the same            ALWIP intra-prediction mode as the corresponding luma block.            -   i. In one example, the same ALWIP intra-prediction mode                is applied on the chroma component if the corresponding                luma block applies the ALWIP mode and the chroma block                is coded with DM mode.            -   ii. In one example, the same ALWIP intra-prediction mode                is applied on the chroma component and the linear                interpolation thereafter can be skipped.            -   iii. In one example, the same ALWIP intra-prediction                mode is applied on the chroma component with a                subsampled matrix and/or bias vector.        -   d. In one example, the number of ALWIP intra-prediction            modes for different component may be different.            -   i. For example, the number of ALWIP intra-prediction                modes for chroma components may be less than that for                luma component for the same block width and height.

Applicability of ALWIP

-   -   14. It is proposed that whether ALWIP can be applied may be        signaled.        -   a. For example, it may be signaled at sequence level (e.g.            in SPS), at picture level (e.g. in PPS or picture header),            at slice level (e.g. in slice header), at tile group level            (e.g. in tile group header), at tile level, at CTU row            level, or at CTU level.        -   b. For example, intra_lwip_flag may not be signaled and            inferred to be 0 if ALWIP cannot be applied.    -   15. It is proposed that whether ALWIP can be applied may depend        on the block width (W) and/or height (H).        -   c. For example, ALWIP may not be applied if W>=T1 (or W>T1)            and H>=T2 (or H>T2). E.g. T1=T2=32;            -   i. For example, ALWIP may not be applied if W<=T1 (or                W<T1) and H<=T2 (or H<T2). E.g. T1=T2=32;        -   d. For example, ALWIP may not be applied if W>=T1 (or W>T1)            or H>=T2 (or H>T2). E.g. T1=T2=32;            -   i. For example, ALWIP may not be applied if W<=T1 (or                W<T1) or H<=T2 (or H<T2). E.g. T1=T2=32;        -   e. For example, ALWIP may not be applied if W+H>=T (or            W*H>T). E.g. T=256;            -   i. For example, ALWIP may not be applied if W+H<=T (or                W+H<T). E.g. T=256;        -   f. For example, ALWIP may not be applied if W*H>=T (or            W*H>T). E.g. T=256;            -   i. For example, ALWIP may not be applied if W*H<=T (or                W*H<T). E.g. T=256;        -   g. For example, intra_lwip_flag may not be signaled and            inferred to be 0 if ALWIP cannot be applied.

Calculation Problems in ALWIP

-   -   16. It is proposed that any shift operation involved in ALWIP        can only left shift or right shift a number by S, where S must        be larger or equal to 0.        -   a. In one example, the right shift operation may be            different when S is equal to 0 or larger than 0.            -   i. In one example, upsBdryX[x] should be calculated as

upsBdryX[x]=(Σ_(i=0) ^(uDwn-1) refX[x*uDwn+i]+(1<<(Log 2(uDwn)−1)))>>Log2(uDwn)whenuDwn>1, and

upsBdryX[x]=Σ_(i=0) ^(uDwn-1) refX[x*uDwn+i]whenuDwn is equal to1.

-   -   -   b. In one example, upsBdryX[x] should be calculated as

upsBdryX[x]=(Σ_(i=0) ^(uDwn-1) refX[x*uDwn+i]+(1<<Log 2(uDwn)>>1))>>Log2(uDwn)

-   -   17. It is proposed that the results should be rounded        toward-zero or away-from-zero in the up-sampling process of        ALWIP.        -   a. In one example,

predSamples[xHor+dX][yHor]((upHor−dX)*predSamples[xHor][yHor]+dX*predSamples[xHor+upHor][yHor]+offsetHor)/upHor  (8-X39)

and

predSamples[xVer][yVer+dY]((upVer−dY)*predSamples[xVer][yVer]+dY*predSamples[xVer][yVer+upVer]+offsetVer)/upVer  (8-X40)

-   -   -   where offsetHor and offsetVer are integers. For example,            offsetHor=upHor/2 and offsetVer-upVer/2.            Interaction with Other Coding Tools

    -   18. It is proposed that ALWIP may be used for a CIIP-coded        block.        -   a. In one example, in a CIIP-coded block, it may be            explicitly signaled whether an ALWIP intra-prediction mode            or a normal intra prediction mode such as Planar is used to            generate the intra prediction signal.        -   b. In one example, it may be implicitly inferred whether an            ALWIP intra-prediction mode or a normal intra prediction            mode such as Planar may be used to generate the intra            prediction signal.            -   i. In one example, ALWIP intra-prediction mode may never                be used in a CIIP coded block.                -   1) Alternatively, normal intra prediction may never                    be used in a CIIP coded block.            -   ii. In one example, it may be inferred from information                of neighboring blocks whether an ALWIP intra-prediction                mode or a normal intra prediction mode such as Planar is                used to generate the intra prediction signal.

    -   19. It is proposed that the whole or partial of the procedure        used to down-sample the neighboring luma samples in the CCLM        mode may be used to down-sample the neighboring samples in the        ALWIP mode.        -   a. Alternatively, the whole or partial of the procedure used            to down-sample the neighboring luma samples in the ALWIP            mode may be used to down-sample the neighboring samples in            the CCLM mode.        -   b. The down-sampling procedure may be invoked with different            parameters/arguments when it is used in the CCLM process and            ALWIP process.        -   c. In one example, the down-sampling method (such as            selection of neighboring luma locations, down-sampling            filters) in the CCLM process may be utilized in the ALWIP            process.        -   d. The procedure used to down-sample the neighboring luma            samples at least include the selection of down-sampled            positions, the down-sampling filters, the rounding and            clipping operations.

    -   20. It is proposed that a block coded with ALWIP mode cannot        apply RST or/and secondary transform or/and rotation transform        or/and Non-Separable Secondary Transform (NSST).        -   a. In one example, whether such constraint may be applied or            not may depend on the dimension information of the block,            e.g., same as conditions described in (15).        -   b. Alternatively, ALWIP mode may be disallowed when RST            or/and secondary transform or/and rotation transform or/and            NSST is applied.        -   c. Alternatively, a block coded with ALWIP mode may apply            RST or/and secondary transform or/and rotation transform            or/and Non-Separable Secondary Transform (NSST).            -   i. In one example, the selection of transform matrix may                depend the ALWIP intra-prediction mode.            -   ii. In one example, the selection of transform matrix                may depend the normal intra-prediction mode which is                converted from the ALWIP intra-prediction mode.            -   iii. In one example, the selection of transform matrix                may depend the classification on the normal                intra-prediction mode which is converted from the ALWIP                intra-prediction mode.

    -   21. It is proposed that a block coded with ALWIP mode cannot        apply Block-based DPCM (BDPCM) or Residue RDPCM.        -   a. Alternatively, ALWIP mode may be disallowed when BDPCM or            RDPCM is applied.

    -   22. It is proposed that a block coded with ALWIP mode may only        use DCT-II as the transform.        -   a. In one example, the signalling of transform matrix            indices is always skipped.        -   b. Alternatively, it is proposed that the transform used for            a block coded with ALWIP mode may be implicitly derived            instead of explicitly signaled. For example, the transform            may be selected following the way proposed in JVET-M0303.        -   c. Alternatively, it is proposed that a block coded with            ALWIP mode may only use transform skip.            -   i. Alternatively, furthermore, when ALWIP is used, the                signalling of indication of usage of transform skip is                skipped.        -   d. In one example, ALWIP mode information (such as            enabled/disabled, prediction mode index) may be            conditionally signalled after indications of transform            matrix.            -   i. In one example, for a given transform matrix (such as                transform skip or DCT-II), the indications of ALWIP mode                information may be signalled.            -   ii. Alternatively, furthermore, the indications of ALWIP                mode information may be skipped for some pre-defined                transform matrices.

    -   23. It is proposed that a block coded with ALWIP mode is        regarded to be coded with a normal intra-prediction converted        from the ALWIP intra-prediction mode when the selected transform        is mode-dependent.

    -   24. ALWIP mode may not use transform skip.        -   a. For example, there is no need to further signal the            indication of usage of transform skip in this case.        -   b. Alternatively, ALWIP mode may be disallowed when            transform skip is applied.            -   i. For example, there is no need to signal ALWIP mode                information when transform skip is applied in this case.

    -   25. In the filtering process, such as deblocking filter, sample        adaptive offset (SAO), adaptive loop filter (ALF), how to select        the filters and/or whether to filter samples may be determined        by the usage of ALWIP.

    -   26. Unfiltered neighboring samples may be used in ALWIP mode.        -   a. Alternatively, filtered neighboring samples may be used            in ALWIP mode.        -   b. In one example, filtered neighboring samples may be used            for down sampling and unfiltered neighboring samples may be            used for up sampling.        -   c. In one example, unfiltered neighboring samples may be            used for down sampling and filtered neighboring samples may            be used for up sampling.        -   d. In one example, filtered left neighboring samples may be            used in up sampling and unfiltered above neighboring samples            may be used in up sampling.        -   e. In one example, unfiltered left neighboring samples may            be used in up sampling and filtered above neighboring            samples may be used in up sampling.        -   f. In one example, whether filter or unfiltered neighboring            samples is used may depend on the ALWIP mode.            -   i. In one example, ALWIP mode may be converted to                traditional intra prediction mode, and whether filtered                or unfiltered neighboring samples is used may depend on                the converted traditional intra prediction mode. For                example, such decision is same as traditional intra                prediction modes.            -   ii. Alternatively, whether filter or unfiltered                neighboring samples is used for ALWIP mode may be                signaled.        -   g. In one example, the filtered samples may be generated            same as traditional intra prediction modes.

    -   27. Which matrices or/and offset vectors are used may depend on        reshaping (a.k.a. LMCS, luma mapping with chroma scaling)        information.        -   a. In one example, different matrices or/and offset vectors            may be used when reshaping is on and off.        -   b. In one example, different matrices or/and offset vectors            may be used for different reshaping parameters.        -   c. In one example, ALWIP may be always performed in original            domain.            -   i. For example, neighboring sample are mapped to the                original domain (if reshaping is applied) before used in                ALWIP.

    -   28. ALWIP may be disabled when reshaping is applied.        -   a. Alternatively, reshaping may be disabled when ALWIP is            enabled.        -   b. In one example, ALWIP may be disabled for HDR (high            dynamic range) content when reshaping is applied.

    -   29. The matrices used in ALWIP may depend on sample bit-depth.        -   a. Alternatively, furthermore, the offset values used in            ALWIP may depend on sample bit-depth.        -   b. Alternatively, the matrix parameters and offset values            can be stored in M-bit precision for N-bit samples (M<=N),            e.g., the matrix parameters and offset values can be stored            in 8-bit precision for a 10-bit sample.        -   c. The sample bit-depth may be the bit-depth of input array            for a color component such as luma.        -   d. The sample bit-depth may be the bit-depth of internal            array/reconstructed sample for a color component, such as            luma.

    -   30. The matrix parameters and/or offset values for a specified        block size may be derived from the matrix parameters and/or        offset values for other block sizes.

    -   31. In one example, the 16×8 matrix of 8×8 block can be derived        from the 16×4 matrix of 4×4 block.

    -   32. It is proposed that the prediction generated by ALWIP may be        treated as an intermedium signal which will be processed to        obtain the prediction signal to be further used.        -   a. In one example, Position Dependent Intra Prediction            Combination (PDPC) may be applied on the prediction            generated by ALWIP to generate the prediction signal to be            further used.            -   i. In one example, PDPC is done on an ALWIP coded block                in the same way as the block is coded with a specific                normal intra-prediction mode, such as Planar or DC.            -   ii. In one example, PDPC is done on an ALWIP coded block                in the same way as the block coded with a normal                intra-prediction mode which is converted from the ALWIP                intra-prediction mode.            -   iii. In one example, PDPC is applied on an ALWIP coded                block conditionally.                -   1) For example, PDPC is applied on an ALWIP coded                    block only when PDPC is applied on the normal                    intra-prediction mode which is converted from the                    ALWIP intra-prediction mode.        -   b. In one example, the boundary samples prediction generated            by ALWIP may be filtered with neighbouring samples to            generate the prediction signal to be further used.            -   i. In one example, filtering on boundary samples is done                on an ALWIP coded block in the same way as the block is                coded with a specific normal intra-prediction mode, such                as Planar or DC.            -   ii. In one example, filtering on boundary samples is                done on an ALWIP coded block in the same way as the                block coded with a normal intra-prediction mode which is                converted from the ALWIP intra-prediction mode.            -   iii. In one example, filtering on boundary samples is                applied on an ALWIP coded block conditionally.                -   1) For example, filtering on boundary samples is                    applied on an ALWIP coded block only when filtering                    on boundary samples is applied on the normal                    intra-prediction mode which is converted from the                    ALWIP intra-prediction mode.

    -   33. It is proposed that interpolation filters other than        bilinear interpolation filter may be used in the up-sampling        process of ALWIP.        -   a. In one example, 4-tap interpolation filters may be used            in the up-sampling process of ALWIP.            -   i. For example, the 4-tap interpolation filters in VVC                used to do the motion compensation for chroma components                may be used in the up-sampling process of ALWIP.            -   ii. For example, the 4-tap interpolation filters in VVC                used to do angular intra-prediction may be used in the                up-sampling process of ALWIP.            -   iii. For example, the 8-tap interpolation filters in VVC                used to do the motion compensation for luma component                may be used in the up-sampling process of ALWIP.

    -   34. Samples within a block coded in ALWIP mode may be predicted        in different ways.        -   a. In one example, for a W*H block, prediction of a sW*sH            sub-block within it may be generated by applying sW*sH ALWIP            to it.            -   i. In one example, for a W*H block, prediction of its                top-left W/2*H/2 block may be generated by applying                W/2*H/2 ALWIP to it.            -   ii. In one example, for a W*H block, prediction of its                left W/2*H block may be generated by applying W/2*H                ALWIP to it.            -   iii. In one example, for a W*H block, prediction of its                top W*H/2 block may be generated by applying W*H/2 ALWIP                to it.            -   iv. In one example, the sW*sH sub-block may have                available left or/and above neighboring samples.        -   b. In one example, how to decide the position of the            sub-block may depend on dimension of the block.            -   i. For example, when W>=H, prediction of its left W/2*H                block may be generated by applying W/2*H ALWIP to it.            -   ii. For example, when H>=W, prediction of its top W*H/2                block may be generated by applying W*H/2 ALWIP to it.            -   iii. For example, when W is equal to H, prediction of                its top-left W/2*H/2 block may be generated by applying                W/2*H/2 ALWIP to it.        -   c. In one example, furthermore, prediction of the remaining            samples (e.g., samples do not belong to the sW*sH sub-block)            may be generated by applying the W*H ALWIP.            -   i. Alternatively, prediction of the remaining samples                may be generated by applying conventional intra                prediction (e.g., using the converted intra prediction                mode as the intra mode).            -   ii. Furthermore, calculation may be skipped for samples                in the sW*sH sub-block.

    -   35. Samples within a block coded in ALWIP mode may be predicted        in sub-block (e.g., with size sW*sH) level.        -   a. In one example, sW*sH ALWIP may be applied to each            sub-block using neighboring reconstructed samples (e.g., for            boundary sub-blocks) or/and neighboring predicted samples            (e.g., for inner sub-blocks).        -   b. In one example, sub-blocks may be predicted in            raster-scan order.        -   c. In one example, sub-blocks may be predicted in zigzag            order.        -   d. In one example, width (height) of sub-blocks may be no            larger than sWMax (sHMax).        -   e. In one example, when a block with either width or height            or both width and height are both larger than (or equal to)            a threshold L, the block may be split into multiple            sub-blocks.        -   f. The threshold L may be pre-defined or signaled in            SPS/PPS/picture/slice/tile group/tile level.            -   i. Alternatively, the thresholds may depend on certain                coded information, such as block size, picture type,                temporal layer index, etc. al.

    -   36. It is proposed that the neighbouring samples (adjacent or        non-adjacent) are filtered before being used in ALWIP.        -   a. Alternatively, neighbouring samples are not filtered            before being used in ALWIP.        -   b. Alternatively, neighbouring samples are conditionally            filtered before being used in ALWIP.            -   i. For example, neighbouring samples are filtered before                being used in ALWIP only when the ALWIP intra-prediction                mode is equal to one or some specific values.

The examples described above may be incorporated in the context of themethods described below, e.g., methods 1100-1400 and 2000-2300, whichmay be implemented at a video encoder and/or decoder.

FIG. 11 shows a flowchart of an exemplary method for video processing.The method 1100 includes, at step 1110, determining that a current videoblock is coded using an affine linear weighted intra prediction (ALWIP)mode.

The method 1100 includes, at step 1120, constructing, based on thedetermining, at least a portion of a most probable mode (MPM) list forthe ALWIP mode based on an at least a portion of an MPM list for anon-ALWIP intra mode.

The method 1100 includes, at step 1130, performing, based on the MPMlist for the ALWIP mode, a conversion between the current video blockand a bitstream representation of the current video block.

In some embodiments, a size of the MPM list of the ALWIP mode isidentical to a size of the MPM list for the non-ALWIP intra mode. In anexample, the size of the MPM list of the ALWIP mode is 6.

In some embodiments, the method 1100 further comprises the step ofinserting default modes to the MPM list for the ALWIP mode. In anexample, the default modes are inserted prior to the portion of a MPMlist for the ALWIP mode that is based on the MPM list for the non-ALWIPintra mode. In another example, the default modes are insertedsubsequent to the portion of a MPM list for the ALWIP mode that is basedon the MPM list for the non-ALWIP intra mode. In yet another example,the default modes are inserted in an interleaved manner with the portionof a MPM list for the ALWIP mode that is based on the MPM list for thenon-ALWIP intra mode.

In some embodiments, constructing the MPM list for the ALWIP mode andthe MPM list for the non-ALWIP intra mode is based on one or moreneighboring blocks.

In some embodiments, constructing the MPM list for the ALWIP mode andthe MPM list for the non-ALWIP intra mode is based a height or a widthof the current video block.

In some embodiments, constructing the MPM list for the ALWIP mode isbased on a first set of parameters that is different from a second setof parameters used to construct the MPM list for the non-ALWIP intramode.

In some embodiments, the method 1100 further includes the step ofdetermining that a neighboring block of the current video block has beencoded with the ALWIP mode, and designating, in constructing the MPM listfor the non-ALWIP intra mode, the neighboring block as unavailable.

In some embodiments, the method 1100 further includes the step ofdetermining that a neighboring block of the current video block has beencoded with the non-ALWIP intra mode, and designating, in constructingthe MPM list for the ALWIP mode, the neighboring block as unavailable.

In some embodiments, the non-ALWIP intra mode is based on a normal intramode, a multiple reference line (MRL) intra prediction mode or an intrasub-partition (ISP) tool.

FIG. 12 shows a flowchart of an exemplary method for video processing.The method 1200 includes, at step 1210, determining that a lumacomponent of a current video block is coded using an affine linearweighted intra prediction (ALWIP) mode.

The method 1200 includes, at step 1220, inferring, based on thedetermining, a chroma intra mode.

The method 1200 includes, at step 1230, performing, based on the chromaintra mode, a conversion between the current video block and a bitstreamrepresentation of the current video block.

In some embodiments, the luma component covers a predetermined chromasample of the chroma component. In an example, the predetermined chromasample is a top-left sample or a center sample of the chroma component.

In some embodiments, the inferred chroma intra mode is a DM mode.

In some embodiments, the inferred chroma intra mode is the ALWIP mode.

In some embodiments, the ALWIP mode is applied to one or more chromacomponents of the current video block.

In some embodiments, different matrix or bias vectors of the ALWIP modeare applied to different color components of the current video block. Inan example, the different matrix or bias vectors are predefined jointlyfor Cb and Cr components. In another example, the Cb and Cr componentsare concatenated. In yet another example, the Cb and Cr components areinterleaved.

FIG. 13 shows a flowchart of an exemplary method for video processing.The method 1300 includes, at step 1310, determining that a current videoblock is coded using an affine linear weighted intra prediction (ALWIP)mode.

The method 1300 includes, at step 1320, performing, based on thedetermining, a conversion between the current video block and abitstream representation of the current video block.

In some embodiments, the determining is based on signaling in a sequenceparameter set (SPS), a picture parameter set (PPS), a slice header, atile group header, a tile header, a coding tree unit (CTU) row or a CTUregion.

In some embodiments, the determining is based on a height (H) or a width(W) of the current video block. In an example, W>T1 or H>T2. In anotherexample, W≥T1 or H≥T2. In yet another example, W<T1 or H<T2. In yetanother example, W≤T1 or H≤T2. In yet another example, T1=32 and T2=32.

In some embodiments, the determining is based on a height (H) or a width(W) of the current video block. In an example, W+H≤T. In anotherexample, W+H≥T. In yet another example, W×H≤T. In yet another example,W×H≥T. In yet another example, T=256.

FIG. 14 shows a flowchart of an exemplary method for video processing.The method 1400 includes, at step 1410, determining that a current videoblock is coded using a coding mode different from an affine linearweighted intra prediction (ALWIP) mode.

The method 1400 includes, at step 1420, performing, based on thedetermining, a conversion between the current video block and abitstream representation of the current video block.

In some embodiments, the coding mode is a combined intra and interprediction (CIIP) mode, and method 1400 further includes the step ofperforming a selection between the ALWIP mode and a normal intraprediction mode. In an example, performing the selection is based on anexplicit signaling in the bitstream representation of the current videoblock. In another example, performing the selection is based onpredetermined rule. In yet another example, the predetermined rulealways selects the ALWIP mode when the current video block is codedusing the CIIP mode. In yet another example, the predetermined rulealways selects the normal intra prediction mode when the current videoblock is coded using the CIIP mode.

In some embodiments, the coding mode is a cross-component linear model(CCLM) prediction mode. In an example, a downsampling procedure for theALWIP mode is based on a downsampling procedure for the CCLM predictionmode. In another example, the downsampling procedure for the ALWIP modeis based on a first set of parameters, and wherein the downsamplingprocedure for the CCLM prediction mode is based on a second set ofparameters different from the first set of parameters. In yet anotherexample, the downsampling procedure for the ALWIP mode or the CCLMprediction mode comprises at least one of a selection of downsampledpositions, a selection of downsampling filters, a rounding operation ora clipping operation.

In some embodiments, the method 1400 further includes the step ofapplying one or more of a Reduced Secondary Transform (RST), a secondarytransform, a rotation transform or a Non-Separable Secondary Transform(NSST).

In some embodiments, the method 1400 further includes the step ofapplying block-based differential pulse coded modulation (DPCM) orresidual DPCM.

6 Example Implementations of the Disclosed Technology

FIG. 15 is a block diagram of a video processing apparatus 1500. Theapparatus 1500 may be used to implement one or more of the methodsdescribed herein. The apparatus 1500 may be embodied in a smartphone,tablet, computer, Internet of Things (IoT) receiver, and so on. Theapparatus 1500 may include one or more processors 1502, one or morememories 1504 and video processing hardware 1506. The processor(s) 1502may be configured to implement one or more methods (including, but notlimited to, methods 1100 to 1400 and 2000 to 2300) described in thepresent document. The memory (memories) 1504 may be used for storingdata and code used for implementing the methods and techniques describedherein. The video processing hardware 1506 may be used to implement, inhardware circuitry, some techniques described in the present document.

In some embodiments, the video coding methods may be implemented usingan apparatus that is implemented on a hardware platform as describedwith respect to FIG. 15.

FIG. 16 is a block diagram showing an example video processing system1600 in which various techniques disclosed herein may be implemented.Various implementations may include some or all of the components of thesystem 1600. The system 1600 may include input 1602 for receiving videocontent. The video content may be received in a raw or uncompressedformat, e.g., 8 or 10 bit multi-component pixel values, or may be in acompressed or encoded format. The input 1602 may represent a networkinterface, a peripheral bus interface, or a storage interface. Examplesof network interface include wired interfaces such as Ethernet, passiveoptical network (PON), etc. and wireless interfaces such as Wi-Fi orcellular interfaces.

The system 1600 may include a coding component 1604 that may implementthe various coding or encoding methods described in the presentdocument. The coding component 1604 may reduce the average bitrate ofvideo from the input 1602 to the output of the coding component 1604 toproduce a coded representation of the video. The coding techniques aretherefore sometimes called video compression or video transcodingtechniques. The output of the coding component 1604 may be eitherstored, or transmitted via a communication connected, as represented bythe component 1606. The stored or communicated bitstream (or coded)representation of the video received at the input 1602 may be used bythe component 1608 for generating pixel values or displayable video thatis sent to a display interface 1610. The process of generatinguser-viewable video from the bitstream representation is sometimescalled video decompression. Furthermore, while certain video processingoperations are referred to as “coding” operations or tools, it will beappreciated that the coding tools or operations are used at an encoderand corresponding decoding tools or operations that reverse the resultsof the coding will be performed by a decoder.

Examples of a peripheral bus interface or a display interface mayinclude universal serial bus (USB) or high definition multimediainterface (HDMI) or Displayport, and so on. Examples of storageinterfaces include SATA (serial advanced technology attachment), PCI,IDE interface, and the like. The techniques described in the presentdocument may be embodied in various electronic devices such as mobilephones, laptops, smartphones or other devices that are capable ofperforming digital data processing and/or video display.

Some embodiments of the disclosed technology include making a decisionor determination to enable a video processing tool or mode. In anexample, when the video processing tool or mode is enabled, the encoderwill use or implement the tool or mode in the processing of a block ofvideo, but may not necessarily modify the resulting bitstream based onthe usage of the tool or mode. That is, a conversion from the block ofvideo to the bitstream representation of the video will use the videoprocessing tool or mode when it is enabled based on the decision ordetermination. In another example, when the video processing tool ormode is enabled, the decoder will process the bitstream with theknowledge that the bitstream has been modified based on the videoprocessing tool or mode. That is, a conversion from the bitstreamrepresentation of the video to the block of video will be performedusing the video processing tool or mode that was enabled based on thedecision or determination.

Some embodiments of the disclosed technology include making a decisionor determination to disable a video processing tool or mode. In anexample, when the video processing tool or mode is disabled, the encoderwill not use the tool or mode in the conversion of the block of video tothe bitstream representation of the video. In another example, when thevideo processing tool or mode is disabled, the decoder will process thebitstream with the knowledge that the bitstream has not been modifiedusing the video processing tool or mode that was disabled based on thedecision or determination.

FIG. 17 is a block diagram that illustrates an example video codingsystem 100 that may utilize the techniques of this disclosure. As shownin FIG. 17, video coding system 100 may include a source device 110 anda destination device 120. Source device 110 generates encoded video datawhich may be referred to as a video encoding device. Destination device120 may decode the encoded video data generated by source device 110which may be referred to as a video decoding device. Source device 110may include a video source 112, a video encoder 114, and an input/output(I/O) interface 116.

Video source 112 may include a source such as a video capture device, aninterface to receive video data from a video content provider, and/or acomputer graphics system for generating video data, or a combination ofsuch sources. The video data may comprise one or more pictures. Videoencoder 114 encodes the video data from video source 112 to generate abitstream. The bitstream may include a sequence of bits that form acoded representation of the video data. The bitstream may include codedpictures and associated data. The coded picture is a codedrepresentation of a picture. The associated data may include sequenceparameter sets, picture parameter sets, and other syntax structures. I/Ointerface 116 may include a modulator/demodulator (modem) and/or atransmitter. The encoded video data may be transmitted directly todestination device 120 via I/O interface 116 through network 130 a. Theencoded video data may also be stored onto a storage medium/server 130 bfor access by destination device 120.

Destination device 120 may include an I/O interface 126, a video decoder124, and a display device 122.

I/O interface 126 may include a receiver and/or a modem. I/O interface126 may acquire encoded video data from the source device 110 or thestorage medium/server 130 b. Video decoder 124 may decode the encodedvideo data. Display device 122 may display the decoded video data to auser. Display device 122 may be integrated with the destination device120, or may be external to destination device 120 which be configured tointerface with an external display device.

Video encoder 114 and video decoder 124 may operate according to a videocompression standard, such as the High Efficiency Video Coding (HEVC)standard, Versatile Video Coding(VVM) standard and other current and/orfurther standards.

FIG. 18 is a block diagram illustrating an example of video encoder 200,which may be video encoder 114 in the system 100 illustrated in FIG. 17.

Video encoder 200 may be configured to perform any or all of thetechniques of this disclosure. In the example of FIG. 18, video encoder200 includes a plurality of functional components. The techniquesdescribed in this disclosure may be shared among the various componentsof video encoder 200. In some examples, a processor may be configured toperform any or all of the techniques described in this disclosure.

The functional components of video encoder 200 may include a partitionunit 201, a predication unit 202 which may include a mode select unit203, a motion estimation unit 204, a motion compensation unit 205 and anintra prediction unit 206, a residual generation unit 207, a transformunit 208, a quantization unit 209, an inverse quantization unit 210, aninverse transform unit 211, a reconstruction unit 212, a buffer 213, andan entropy encoding unit 214.

In other examples, video encoder 200 may include more, fewer, ordifferent functional components. In an example, predication unit 202 mayinclude an intra block copy(IBC) unit. The IBC unit may performpredication in an IBC mode in which at least one reference picture is apicture where the current video block is located.

Furthermore, some components, such as motion estimation unit 204 andmotion compensation unit 205 may be highly integrated, but arerepresented in the example of FIG. 18 separately for purposes ofexplanation.

Partition unit 201 may partition a picture into one or more videoblocks. Video encoder 200 and video decoder 300 may support variousvideo block sizes.

Mode select unit 203 may select one of the coding modes, intra or inter,e.g., based on error results, and provide the resulting intra- orinter-coded block to a residual generation unit 207 to generate residualblock data and to a reconstruction unit 212 to reconstruct the encodedblock for use as a reference picture. In some example, Mode select unit203 may select a combination of intra and inter predication (CIIP) modein which the predication is based on an inter predication signal and anintra predication signal. Mode select unit 203 may also select aresolution for a motion vector (e.g., a sub-pixel or integer pixelprecision) for the block in the case of inter-predication.

To perform inter prediction on a current video block, motion estimationunit 204 may generate motion information for the current video block bycomparing one or more reference frames from buffer 213 to the currentvideo block. Motion compensation unit 205 may determine a predictedvideo block for the current video block based on the motion informationand decoded samples of pictures from buffer 213 other than the pictureassociated with the current video block.

Motion estimation unit 204 and motion compensation unit 205 may performdifferent operations for a current video block, for example, dependingon whether the current video block is in an I slice, a P slice, or a Bslice.

In some examples, motion estimation unit 204 may perform uni-directionalprediction for the current video block, and motion estimation unit 204may search reference pictures of list 0 or list 1 for a reference videoblock for the current video block. Motion estimation unit 204 may thengenerate a reference index that indicates the reference picture in list0 or list 1 that contains the reference video block and a motion vectorthat indicates a spatial displacement between the current video blockand the reference video block. Motion estimation unit 204 may output thereference index, a prediction direction indicator, and the motion vectoras the motion information of the current video block. Motioncompensation unit 205 may generate the predicted video block of thecurrent block based on the reference video block indicated by the motioninformation of the current video block.

In other examples, motion estimation unit 204 may perform bi-directionalprediction for the current video block, motion estimation unit 204 maysearch the reference pictures in list 0 for a reference video block forthe current video block and may also search the reference pictures inlist 1 for another reference video block for the current video block.Motion estimation unit 204 may then generate reference indexes thatindicate the reference pictures in list 0 and list 1 containing thereference video blocks and motion vectors that indicate spatialdisplacements between the reference video blocks and the current videoblock. Motion estimation unit 204 may output the reference indexes andthe motion vectors of the current video block as the motion informationof the current video block. Motion compensation unit 205 may generatethe predicted video block of the current video block based on thereference video blocks indicated by the motion information of thecurrent video block.

In some examples, motion estimation unit 204 may output a full set ofmotion information for decoding processing of a decoder.

In some examples, motion estimation unit 204 may do not output a fullset of motion information for the current video. Rather, motionestimation unit 204 may signal the motion information of the currentvideo block with reference to the motion information of another videoblock. For example, motion estimation unit 204 may determine that themotion information of the current video block is sufficiently similar tothe motion information of a neighboring video block.

In one example, motion estimation unit 204 may indicate, in a syntaxstructure associated with the current video block, a value thatindicates to the video decoder 300 that the current video block has thesame motion information as the another video block.

In another example, motion estimation unit 204 may identify, in a syntaxstructure associated with the current video block, another video blockand a motion vector difference (MVD). The motion vector differenceindicates a difference between the motion vector of the current videoblock and the motion vector of the indicated video block. The videodecoder 300 may use the motion vector of the indicated video block andthe motion vector difference to determine the motion vector of thecurrent video block.

As discussed above, video encoder 200 may predictively signal the motionvector. Two examples of predictive signaling techniques that may beimplemented by video encoder 200 include advanced motion vectorpredication (AMVP) and merge mode signaling.

Intra prediction unit 206 may perform intra prediction on the currentvideo block. When intra prediction unit 206 performs intra prediction onthe current video block, intra prediction unit 206 may generateprediction data for the current video block based on decoded samples ofother video blocks in the same picture. The prediction data for thecurrent video block may include a predicted video block and varioussyntax elements.

Residual generation unit 207 may generate residual data for the currentvideo block by subtracting (e.g., indicated by the minus sign) thepredicted video block(s) of the current video block from the currentvideo block. The residual data of the current video block may includeresidual video blocks that correspond to different sample components ofthe samples in the current video block.

In other examples, there may be no residual data for the current videoblock for the current video block, for example in a skip mode, andresidual generation unit 207 may not perform the subtracting operation.

Transform processing unit 208 may generate one or more transformcoefficient video blocks for the current video block by applying one ormore transforms to a residual video block associated with the currentvideo block.

After transform processing unit 208 generates a transform coefficientvideo block associated with the current video block, quantization unit209 may quantize the transform coefficient video block associated withthe current video block based on one or more quantization parameter (QP)values associated with the current video block.

Inverse quantization unit 210 and inverse transform unit 211 may applyinverse quantization and inverse transforms to the transform coefficientvideo block, respectively, to reconstruct a residual video block fromthe transform coefficient video block. Reconstruction unit 212 may addthe reconstructed residual video block to corresponding samples from oneor more predicted video blocks generated by the predication unit 202 toproduce a reconstructed video block associated with the current blockfor storage in the buffer 213.

After reconstruction unit 212 reconstructs the video block, loopfiltering operation may be performed reduce video blocking artifacts inthe video block.

Entropy encoding unit 214 may receive data from other functionalcomponents of the video encoder 200. When entropy encoding unit 214receives the data, entropy encoding unit 214 may perform one or moreentropy encoding operations to generate entropy encoded data and outputa bitstream that includes the entropy encoded data.

FIG. 19 is a block diagram illustrating an example of video decoder 300which may be video decoder 114 in the system 100 illustrated in FIG. 17.

The video decoder 300 may be configured to perform any or all of thetechniques of this disclosure. In the example of FIG. 19, the videodecoder 300 includes a plurality of functional components. Thetechniques described in this disclosure may be shared among the variouscomponents of the video decoder 300. In some examples, a processor maybe configured to perform any or all of the techniques described in thisdisclosure.

In the example of FIG. 19, video decoder 300 includes an entropydecoding unit 301, a motion compensation unit 302, an intra predictionunit 303, an inverse quantization unit 304, an inverse transformationunit 305, and a reconstruction unit 306 and a buffer 307. Video decoder300 may, in some examples, perform a decoding pass generally reciprocalto the encoding pass described with respect to video encoder 200 (FIG.18).

Entropy decoding unit 301 may retrieve an encoded bitstream. The encodedbitstream may include entropy coded video data (e.g., encoded blocks ofvideo data). Entropy decoding unit 301 may decode the entropy codedvideo data, and from the entropy decoded video data, motion compensationunit 302 may determine motion information including motion vectors,motion vector precision, reference picture list indexes, and othermotion information. Motion compensation unit 302 may, for example,determine such information by performing the AMVP and merge mode.

Motion compensation unit 302 may produce motion compensated blocks,possibly performing interpolation based on interpolation filters.Identifiers for interpolation filters to be used with sub-pixelprecision may be included in the syntax elements.

Motion compensation unit 302 may use interpolation filters as used byvideo encoder 20 during encoding of the video block to calculateinterpolated values for sub-integer pixels of a reference block. Motioncompensation unit 302 may determine the interpolation filters used byvideo encoder 200 according to received syntax information and use theinterpolation filters to produce predictive blocks.

Motion compensation unit 302 may uses some of the syntax information todetermine sizes of blocks used to encode frame(s) and/or slice(s) of theencoded video sequence, partition information that describes how eachmacroblock of a picture of the encoded video sequence is partitioned,modes indicating how each partition is encoded, one or more referenceframes (and reference frame lists) for each inter-encoded block, andother information to decode the encoded video sequence.

Intra prediction unit 303 may use intra prediction modes for examplereceived in the bitstream to form a prediction block from spatiallyadjacent blocks. Inverse quantization unit 303 inverse quantizes, i.e.,de-quantizes, the quantized video block coefficients provided in thebitstream and decoded by entropy decoding unit 301. Inverse transformunit 303 applies an inverse transform.

Reconstruction unit 306 may sum the residual blocks with thecorresponding prediction blocks generated by motion compensation unit202 or intra-prediction unit 303 to form decoded blocks. If desired, adeblocking filter may also be applied to filter the decoded blocks inorder to remove blockiness artifacts. The decoded video blocks are thenstored in buffer 307, which provides reference blocks for subsequentmotion compensation/intra predication and also produces decoded videofor presentation on a display device.

In some embodiments, in the ALWIP mode or MIP mode, a prediction blockfor the current video block is determined by a row and column wiseaveraging, followed by a matrix multiplication, followed by aninterpolation to determine the prediction block.

FIG. 20 shows an example flowchart of an example method 2000 formatrix-based intra prediction. Operation 2002 includes performing aconversion between a current video block of a video and a bitstreamrepresentation of the current video block according to a rule, where therule specifies a relationship between samples of the current video blockand matrices or offset values applied in a matrix weighted intraprediction (MIP) mode during the conversion, and where the MIP modeincludes determining a prediction block of the current video block byperforming, on previously coded samples of the video, a boundarydownsampling operation, followed by a matrix vector multiplicationoperation, and selectively followed by an upsampling operation.

In some embodiments for method 2000, the rule specifies that elements ofthe matrices applied in the MIP mode are dependent on a bit-depth of thesamples. In some embodiments for method 2000, the rule specifies thatthe offset values applied in the MIP mode are dependent on a bit-depthof the samples. In some embodiments for method 2000, the rule specifiesthat elements of the matrices and the offset values have a M-bitprecision for the samples having a N-bit precision, wherein M is lessthan or equal to N. In some embodiments for method 2000, M is 8 and N is10. In some embodiments for method 2000, a bit-depth of the samples isthe same as a second bit-depth of an input array for a color component.In some embodiments for method 2000, a bit-depth of the samples is thesame as a second bit-depth of an internal array or a reconstructedsample for a color component. In some embodiments for method 2000, thecolor component includes a luma component. In some embodiments formethod 2000, a first set of parameters for the matrices and/or offsetvalues for the current video block are derived from a second set ofparameters for a second set of matrices and/or second set of offsetvalues of another video block. In some embodiments for method 2000, thecurrent video block includes a 8×8 video block, the another video blockincludes a 4×4 video block, and the first set of parameters for 16×8matrix is derived from the second set of parameters for 16×4 matrix.

FIG. 21 shows an example flowchart of an example method 2100 formatrix-based intra prediction. Operation 2102 includes generating, for acurrent video block, an intermediate prediction block using a matrixweighted intra prediction (MIP) mode in which the intermediateprediction block of the current video block is determined by performing,on previously coded samples of the video, a boundary downsamplingoperation, followed by a matrix vector multiplication operation, andselectively followed by an upsampling operation. Operation 2104 includesgenerating, based on the intermediate prediction block, a finalprediction block based on an additional operation. Operation 2106includes performing, based on the final prediction signal, a conversionbetween the current video block and a bitstream representation of thecurrent video block.

In some embodiments for method 2100, the additional operation is aposition dependent intra prediction combination (PDPC). In someembodiments for method 2100, a first operation comprising the generatingthe final prediction signal using the PDPC is identical to a secondoperation comprising applying the PDPC to a prediction signal generatedusing an intra-prediction mode. In some embodiments for method 2100, theintra-prediction mode includes a planar mode or a DC mode. In someembodiments for method 2100, a first operation comprising the generatingthe final prediction signal using the PDPC is identical to a secondoperation comprising applying the PDPC to a prediction signal generatedusing an intra-prediction mode, and the intra-prediction mode isconverted from the MIP mode.

In some embodiments for method 2100, the PDPC is applied to theintermediate prediction block of the current video block based on arule. In some embodiments for method 2100, the rule indicates that thePDPC is to be applied to the intermediate prediction block of thecurrent video block in response to the PDPC being applied to aprediction signal generated by an intra-prediction mode that isconverted from the MIP mode. In some embodiments for method 2100, theadditional operation is a filtering operation in which boundary samplesof the current video block are filtered with neighboring samples of thecurrent video block. In some embodiments for method 2100, the filteringoperation for filtering the boundary samples of the current video blockcoded with the MIP mode is identical to another filtering operation forfiltering the boundary samples using an intra-prediction mode.

In some embodiments for method 2100, the intra-prediction mode includesa planar mode or a direct current (DC) mode. In some embodiments formethod 2100, the filtering operation for filtering the boundary samplesof the current video block coded with the MIP mode is identical toanother filtering operation for filtering the boundary samples using anintra-prediction mode, and the intra-prediction mode is converted fromthe MIP mode. In some embodiments for method 2100, the filteringoperation is applied based on a rule. In some embodiments for method2100, the rule indicates that the filtering operation is applied tofilter the boundary samples in response to the boundary samples beingfiltered with an intra-prediction mode that is converted from the MIPmode.

FIG. 22 shows an example flowchart of an example method 2200 formatrix-based intra prediction. Operation 2202 includes performing aconversion between a current video block of a video and a bitstreamrepresentation of the current video block, where the conversion includespredicting a plurality of samples of at least a portion of the currentvideo block in a matrix weighted intra prediction (MIP) mode in which aprediction block of the portion of current video block is determined byperforming, on previously coded samples of the video, a boundarydownsampling operation, followed by a matrix vector multiplicationoperation, and selectively followed by an upsampling operation.

In some embodiments for method 2200, the plurality of samples belong toa sub-block of the current video block, the current video block has awidth (W) and a height (H), the sub-block has a width (sW) and a height(sH), and the plurality of samples for the sub-block are predicted byapplying the MIP to the sub-block. In some embodiments for method 2200,the plurality of samples of the sub-block with the width (sW) and theheight (sH) includes left neighboring samples of the current video blockor above neighboring samples of the current video block. In someembodiments for method 2200, the plurality of samples belong to asub-block of the current video block, the current video block has awidth (W) and a height (H), the sub-block is a top left W/2*H/2 block ofthe current video block, and the plurality of samples for the sub-blockare predicted by applying the MIP to the sub-block. In some embodimentsfor method 2200, the plurality of samples belong to a sub-block of thecurrent video block, the current video block has a width (W) and aheight (H), the sub-block is a left W/2*H block of the current videoblock, and the plurality of samples for the sub-block are predicted byapplying the MIP to the sub-block.

In some embodiments for method 2200, the plurality of samples belong toa sub-block of the current video block, the current video block has awidth (W) and a height (H), the sub-block is a top W*H/2 block of thecurrent video block, and the plurality of samples for the sub-block arepredicted by applying the MIP to the sub-block. In some embodiments formethod 2200, the plurality of samples belong to a sub-block of thecurrent video block, the current video block has a width (W) and aheight (H), the sub-block has a width (sW) and a height (sH), and theplurality of samples for the sub-block are predicted by applying the MIPto the sub-block by using left neighboring samples of the current videoblock or by using above neighboring samples of the current video block.

In some embodiments for method 2200, the plurality of samples belong toa sub-block of the current video block, a location of the sub-block isbased on a relationship between a width (W) and a height (H) of thecurrent video block. In some embodiments for method 2200, the sub-blockis a left W/2*H block of the current video block in response to W≥H, andthe plurality of samples for the sub-block are predicted by applying theMIP to the sub-block. In some embodiments for method 2200, the sub-blockis a top W*H/2 block of the current video block in response to H≥W, andthe plurality of samples for the sub-block are predicted by applying theMIP to the sub-block.

In some embodiments for method 2200, the sub-block is a top left W/2*H/2block of the current video block in response to W=H, and the pluralityof samples for the sub-block are predicted by applying the MIP to thesub-block. In some embodiments for method 2200, the plurality of samplesbelong to a sub-block of the current video block, and the method furthercomprises: predicting a second set of samples of the current videoblock, where the second set of samples are located outside of thesub-block, and where the second set of samples are predicted by applyingthe MIP to the current video block.

In some embodiments for method 2200, the plurality of samples belong toa sub-block of the current video block, and where the method furthercomprises: predicting a second set of samples of the current videoblock, where the second set of samples are located outside of thesub-block, where the second set of samples are predicted by applying anintra prediction mode to the current video block, and where the intraprediction mode is converted from the MIP mode. In some embodiments formethod 2200, the plurality of samples belong to a sub-block of thecurrent video block, and where the method further comprises: predictinga second set of samples of the current video block, where the second setof samples are located outside of the sub-block, and where the secondset of samples are predicted by applying the MIP to a region of thecurrent video block that excludes the sub-block.

In some embodiments for method 2200, the plurality of samples belong toat least one sub-block of the current video block. In some embodimentsfor method 2200, for each sub-block, a plurality of samples is predictedby applying the MIP to a sub-block, and for each sub-block, the MIP isapplied to the sub-block by using neighboring reconstructed samples forthe sub-block and/or by using neighboring predicted samples for thesub-block. In some embodiments for method 2200, the neighboringreconstructed samples are used for the sub-block located at a boundaryof the current video block. In some embodiments for method 2200, theneighboring reconstructed samples are used for the sub-block locatedwithin the current video block such that a portion of a boundary of thesub-block is not coextensive with a portion of a boundary of the currentvideo block. In some embodiments for method 2200, the plurality ofsub-blocks are predicted in a raster-scan order. In some embodiments formethod 2200, the plurality of sub-blocks are predicted in a zigzagorder.

In some embodiments for method 2200, a width and a height of the atleast one sub-block is not greater than a maximum width and a maximumheight, respectively. In some embodiments, the method 2200 furthercomprises splitting the current video block into multiple sub-blocks inresponse to any one or more of a width and a height of the current videoblock being greater than or equal to a threshold. In some embodimentsfor method 2200, the threshold is pre-defined. In some embodiments formethod 2200, the threshold is signaled in a sequence parameter set(SPS), picture parameter set (PPS), a picture header, a slice header, atile group header or a tile header. In some embodiments for method 2200,the threshold is based on coded information associated with the currentvideo block. In some embodiments for method 2200, the coded informationincludes a block size of the current video block, a picture type of thecurrent video block, or a temporal layer index of the current videoblock.

FIG. 23 shows an example flowchart of an example method 2300 formatrix-based intra prediction. Operation 2302 includes performing aconversion between a current video block of a video and a bitstreamrepresentation of the current video block, where the conversion is basedon a rule that indicates whether to filter neighboring samples of thecurrent video block prior to applying the matrix weighted intraprediction (MIP) mode during the conversion, and where the MIP modeincludes determining a prediction block of the current video block byperforming, on previously coded samples of the video, a boundarydownsampling operation, followed by a matrix vector multiplicationoperation, and selectively followed by an upsampling operation.

In some embodiments for method 2300, the rule indicates that theneighboring samples are filtered before being used in the MIP mode. Insome embodiments for method 2300, the rule indicates that theneighboring samples are not filtered before being used in the MIP mode.In some embodiments for method 2300, the rule indicates that theneighboring samples are filtered before being used in the MIP mode inresponse to the MIP mode being equal to a particular value.

In the present document, the term “video processing” or “conversion” mayrefer to video encoding, video decoding, video compression or videodecompression. For example, video compression algorithms may be appliedduring conversion from pixel representation of a video to acorresponding bitstream representation or vice versa. The bitstreamrepresentation of a current video block may, for example, correspond tobits that are either co-located or spread in different places within thebitstream, as is defined by the syntax. For example, a macroblock may beencoded in terms of transformed and coded error residual values and alsousing bits in headers and other fields in the bitstream. Furthermore,during conversion, a decoder may parse a bitstream with the knowledgethat some fields may be present, or absent, based on the determination,as is described in the above solutions. Similarly, an encoder maydetermine that certain syntax fields are or are not to be included andgenerate the coded representation accordingly by including or excludingthe syntax fields from the coded representation.

From the foregoing, it will be appreciated that specific embodiments ofthe presently disclosed technology have been described herein forpurposes of illustration, but that various modifications may be madewithout deviating from the scope of the invention. Accordingly, thepresently disclosed technology is not limited except as by the appendedclaims.

Implementations of the subject matter and the functional operationsdescribed in this patent document can be implemented in various systems,digital electronic circuitry, or in computer software, firmware, orhardware, including the structures disclosed in this specification andtheir structural equivalents, or in combinations of one or more of them.Implementations of the subject matter described in this specificationcan be implemented as one or more computer program products, i.e., oneor more modules of computer program instructions encoded on a tangibleand non-transitory computer readable medium for execution by, or tocontrol the operation of, data processing apparatus. The computerreadable medium can be a machine-readable storage device, amachine-readable storage substrate, a memory device, a composition ofmatter effecting a machine-readable propagated signal, or a combinationof one or more of them. The term “data processing unit” or “dataprocessing apparatus” encompasses all apparatus, devices, and machinesfor processing data, including by way of example a programmableprocessor, a computer, or multiple processors or computers. Theapparatus can include, in addition to hardware, code that creates anexecution environment for the computer program in question, e.g., codethat constitutes processor firmware, a protocol stack, a databasemanagement system, an operating system, or a combination of one or moreof them.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, and it can bedeployed in any form, including as a stand-alone program or as a module,component, subroutine, or other unit suitable for use in a computingenvironment. A computer program does not necessarily correspond to afile in a file system. A program can be stored in a portion of a filethat holds other programs or data (e.g., one or more scripts stored in amarkup language document), in a single file dedicated to the program inquestion, or in multiple coordinated files (e.g., files that store oneor more modules, sub programs, or portions of code). A computer programcan be deployed to be executed on one computer or on multiple computersthat are located at one site or distributed across multiple sites andinterconnected by a communication network.

The processes and logic flows described in this specification can beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read only memory ora random access memory or both. The essential elements of a computer area processor for performing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto optical disks, or optical disks. However, a computerneed not have such devices. Computer readable media suitable for storingcomputer program instructions and data include all forms of nonvolatilememory, media and memory devices, including by way of examplesemiconductor memory devices, e.g., EPROM, EEPROM, and flash memorydevices. The processor and the memory can be supplemented by, orincorporated in, special purpose logic circuitry.

It is intended that the specification, together with the drawings, beconsidered exemplary only, where exemplary means an example. As usedherein, the use of “or” is intended to include “and/or”, unless thecontext clearly indicates otherwise.

While this patent document contains many specifics, these should not beconstrued as limitations on the scope of any invention or of what may beclaimed, but rather as descriptions of features that may be specific toparticular embodiments of particular inventions. Certain features thatare described in this patent document in the context of separateembodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Moreover, the separation of various system components in theembodiments described in this patent document should not be understoodas requiring such separation in all embodiments.

Only a few implementations and examples are described and otherimplementations, enhancements and variations can be made based on whatis described and illustrated in this patent document.

What is claimed is:
 1. A method of processing video data, comprising:determining, for a first conversion between a first video block of thevideo and a bitstream of the video, that a first intra mode is appliedon the first video block of the video; deriving reference samples of thefirst video block; performing a boundary downsampling operation on thereference samples of the first video block based on a size of the firstvideo block, followed by a matrix vector multiplication operation, andselectively followed by an upsampling operation to generate predictionsamples for the first video block; and performing the first conversionbased on the prediction samples of the first video block, whereinelements of matrices or offset values applied in the matrix vectormultiplication operation have a fixed precision.
 2. The method of claim1, wherein the fixed precision is an 8-bit precision.
 3. The method ofclaim 1, wherein precision of the first video block and the referencesamples are 10-bit depth.
 4. The method of claim 1, wherein at least twoblocks with different sizes share a matrix with a same size in the firstintra mode.
 5. The method of claim 1, wherein the reference samples arederived without invoking a reference sample filtering operation.
 6. Themethod of claim 1, wherein the reference sample filtering operation isapplied in a normal intra mode which is different from the first intramode.
 7. The method of claim 1, wherein whether the first intra modebeing applied is specified by a first syntax element presented in asequence level and a second syntax element presented in a coding unitlevel.
 8. The method of claim 7, wherein at least one bin of the secondsyntax element is context-based coded.
 9. The method of claim 8, whereinin response to a width-height ratio of the first video block beinggreater than 2, a context with an index of 3 is used for a first bin ofthe second syntax element.
 10. The method of claim 8, wherein inresponse to a width-height ratio of the first video block being smallerthan or equal to 2, a single context selected from contexts with indicesof 0, 1 or 2 is used for a first bin of the second syntax element. 11.The method of claim 1, wherein the boundary downsampling operationincludes deriving, according to a rule, boundary samples by applying aleft bit shift operation or a right bit shift operation on a sum of atleast one reference sample, and wherein the rule determines whether toapply the left bit shift operation or the right bit shift operation. 12.The method of claim 11, wherein the rule defines that the right bitshift operation is applied in response to a number of shifted bits beinggreater than zero.
 13. The method of claim 12, wherein the boundarysamples redBdryS[x] are calculated using one of following equations:redBdryS[x]=(Σ_(i=0) ^(bDwn-1)refS[x*bDwn+i]+(1<<(Log 2(bDwn)−1)))>>Log2(bDwn),if bDwn>1, orredBdryS[x]=refS[x]if bDwn=1, wherein bDwn is equal to a function of thefirst video block size and a boundary size, wherein refS [x] indicates anumber of reference samples x, wherein >>indicates the right bit shiftoperation, and wherein << indicates the left bit shift operation. 14.The method of claim 1, wherein the conversion includes encoding thecurrent video block into the bitstream.
 15. The method of claim 1,wherein the conversion includes decoding the current video block fromthe bitstream.
 16. An apparatus for processing video data comprising aprocessor and a non-transitory memory with instructions thereon, whereinthe instructions upon execution by the processor, cause the processorto: determine, for a first conversion between a first video block of thevideo and a bitstream of the video, that a first intra mode is appliedon the first video block of the video; derive reference samples of thefirst video block; perform a boundary downsampling operation on thereference samples of the first video block based on a size of the firstvideo block, followed by a matrix vector multiplication operation, andselectively followed by an upsampling operation to generate predictionsamples for the first video block; and perform the first conversionbased on the prediction samples of the first video block, whereinelements of matrices or offset values applied in the matrix vectormultiplication operation have a fixed precision.
 17. The apparatus ofclaim 16, wherein the fixed precision is an 8-bit precision.
 18. Theapparatus of claim 16, wherein at least two blocks with different sizesshare a matrix with a same size in the first intra mode.
 19. Anon-transitory computer-readable storage medium storing instructionsthat cause a processor to: determine, for a first conversion between afirst video block of the video and a bitstream of the video, that afirst intra mode is applied on the first video block of the video;derive reference samples of the first video block; perform a boundarydownsampling operation on the reference samples of the first video blockbased on a size of the first video block, followed by a matrix vectormultiplication operation, and selectively followed by an upsamplingoperation to generate prediction samples for the first video block; andperform the first conversion based on the prediction samples of thefirst video block, wherein elements of matrices or offset values appliedin the matrix vector multiplication operation have a fixed precision.20. A non-transitory computer-readable recording medium storing abitstream of a video which is generated by a method performed by a videoprocessing apparatus, wherein the method comprises: determining that afirst intra mode is applied on a first video block of the video;deriving reference samples of the first video block; performing aboundary downsampling operation on the reference samples of the firstvideo block based on a size of the first video block, followed by amatrix vector multiplication operation, and selectively followed by anupsampling operation to generate prediction samples for the first videoblock; and generating the bitstream based on the prediction samples ofthe first video block; wherein elements of matrices or offset valuesapplied in the matrix vector multiplication operation have a fixedprecision.